3,483 research outputs found
Electro-Mechanical Fredericks Effects in Nematic Gels
The solid nematic equivalent of the Fredericks transition is found to depend
on a critical field rather than a critical voltage as in the classical case.
This arises because director anchoring is principally to the solid rubbery
matrix of the nematic gel rather than to the sample surfaces. Moreover, above
the threshold field, we find a competition between quartic (soft) and
conventional harmonic elasticity which dictates the director response. By
including a small degree of initial director misorientation, the calculated
field variation of optical anisotropy agrees well with the conoscopy
measurements of Chang et al (Phys.Rev.E56, 595, 1997) of the electro-optical
response of nematic gels.Comment: Latex (revtex style), 5 EPS figures, submitted to PRE, corrections to
discussion of fig.3, cosmetic change
The physical properties of AM CVn stars: new insights from Gaia DR2
AM CVn binaries are hydrogen deficient compact binaries with an orbital
period in the 5-65 min range and are predicted to be strong sources of
persistent gravitational wave radiation. Using Gaia Data Release 2, we present
the parallaxes and proper motions of 41 out of the 56 known systems. Compared
to the parallax determined using the HST Fine Guidance Sensor we find that the
archetype star, AM CVn, is significantly closer than previously thought. This
resolves the high luminosity and mass accretion rate which models had
difficulty in explaining. Using Pan-STARRS1 data we determine the absolute
magnitude of the AM CVn stars. There is some evidence that donor stars have a
higher mass and radius than expected for white dwarfs or that the donors are
not white dwarfs. Using the distances to the known AM CVn stars we find strong
evidence that a large population of AM CVn stars have still to be discovered.
As this value sets the background to the gravitational wave signal of LISA,
this is of wide interest. We determine the mass transfer rate for 15 AM CVn
stars and find that the majority have a rate significantly greater than
expected from standard models. This is further evidence that the donor star has
a greater size than expected.Comment: Accepted by A&A in main journa
Aging and memory phenomena in magnetic and transport properties of vortex matter: a brief review
There is mounting experimental evidence that strong off-equilibrium
phenomena, such as ``memory'' or ``aging'' effects, play a crucial role in the
physics of vortices in type II superconductors. We give a short review, based
on a recently introduced schematic vortex model, of current progresses in
understanding out of equilibrium vortex behaviours. We develop a unified
description of ``memory'' phenomena in magnetic and transport properties, such
as magnetisation loops and their ``anomalous'' 2nd peak, logarithmic creep,
``anomalous'' finite creep rate in the limit of vanishing temperature,
``memory'' and ``irreversibility'' in I-V characteristics, time dependent
critical currents, ``rejuvenation'' and ``aging'' of the system response.Comment: updated versio
Identification and Environmental Assessments for Different Scenarios of Repurposed Decommissioned Wind Turbine Blades
The rapidly growing wind industry poses a fundamental problem for wind turbine blade (WTB) disposal in many areas of
the world. WTBs are primarily manufactured from composites consisting of a thermoset matrix and reinforcing fibers. Currently,
there are no economically viable recycling technologies available for such large-scale composite products. Thus, other
treatment strategies for disposed WTBs have to be considered. This study explores the repurpose of WTBs as a promising
alternative approach from a processual and technological point of view. For this purpose, the study is guided by the categorization
into four different types of repurposed applications: high-loaded complete structure (T1), low-loaded complete
structure (T2), high-loaded segmented structure (T3), and low-loaded segmented structure (T4). A three-dimensional CAD
model of an Enercon-40/500 (E40) wind turbine blade is derived in a reverse engineering procedure to obtain knowledge
about the actual geometry of the WTB. Based on the design, three ecosystems of product scenarios (S) with different
manufacturing technologies involved are investigated: a climbing tower (S1), a playground (S2) and the combination of a
photovoltaic (PV)-floating pontoon, and a lounger (S3). A screening life cycle assessment (LCA) is conducted to evaluate
the three repurposed scenarios according to environmental aspects. It is shown that the repurpose of E40 WTB composite
material can reduce the environmental impact and leads to significant resource savings in relation to a reference product
of similar quality. A particularly high saving potential is identified for the substitution of emission-intensive materials in
construction applications. Furthermore, it is found that transport processes are the primary contributor to the environmental
impact of repurposed applications
Zwicky Transient Facility constraints on the optical emission from the nearby repeating FRB 180916.J0158+65
The discovery rate of fast radio bursts (FRBs) is increasing dramatically
thanks to new radio facilities. Meanwhile, wide-field instruments such as the
47 deg Zwicky Transient Facility (ZTF) survey the optical sky to study
transient and variable sources. We present serendipitous ZTF observations of
the CHIME repeating source FRB 180916.J0158+65, that was localized to a spiral
galaxy 149 Mpc away and is the first FRB suggesting periodic modulation in its
activity. While 147 ZTF exposures corresponded to expected high-activity
periods of this FRB, no single ZTF exposure was at the same time as a CHIME
detection. No optical source was found at the FRB location in 683
ZTF exposures, totalling 5.69 hours of integration time. We combined ZTF upper
limits and expected repetitions from FRB 180916.J0158+65 in a statistical
framework using a Weibull distribution, agnostic of periodic modulation priors.
The analysis yielded a constraint on the ratio between the optical and radio
fluences of , corresponding to an optical energy erg for a fiducial 10 Jy ms FRB (90%
confidence). A deeper (but less statistically robust) constraint of can be placed assuming a rate of Jy ms)= hr and
FRB occurring during exposures taken in high-activity windows. The
constraint can be improved with shorter per-image exposures and longer
integration time, or observing FRBs at higher Galactic latitudes. This work
demonstrated how current surveys can statistically constrain multi-wavelength
counterparts to FRBs even without deliberately scheduled simultaneous radio
observation.Comment: Accepted for publication in ApJL, 9 pages, 4 figures, 1 tabl
Illuminating Gravitational Waves: A Concordant Picture of Photons from a Neutron Star Merger
Merging neutron stars offer an exquisite laboratory for simultaneously studying strong-field gravity and matter in extreme environments. We establish the physical association of an electromagnetic counterpart (EM170817) to gravitational waves (GW170817) detected from merging neutron stars. By synthesizing a panchromatic dataset, we demonstrate that merging neutron stars are a long-sought production site forging heavy elements by r-process nucleosynthesis. The weak gamma-rays seen in EM170817 are dissimilar to classical short gamma-ray bursts with ultra-relativistic jets. Instead, we suggest that breakout of a wide-angle, mildly-relativistic cocoon engulfing the jet elegantly explains the low-luminosity gamma-rays, the high-luminosity ultraviolet-optical-infrared and the delayed radio/x-ray emission. We posit that all merging neutron stars may lead to a wide-angle cocoon breakout; sometimes accompanied by a successful jet and sometimes a choked jet
The AM Canum Venaticorum binary SDSS J173047.59+554518.5
The AM Canum Venaticorum (AM CVn) binaries are a rare group of hydrogen-deficient, ultrashort period, mass-transferring white dwarf binaries and are possible progenitors of Type Ia supernovae. We present time-resolved spectroscopy of the recently discovered AM CVn binary SDSS J173047.59+554518.5. The average spectrum shows strong double-peaked helium emission lines, as well as a variety of metal lines, including neon; this is the second detection of neon in an AM CVn binary, after the much brighter system GP Com. We detect no calcium in the accretion disc, a puzzling feature that has been noted in many of the longer period AM CVn binaries. We measure an orbital period, from the radial velocities of the emission lines, of 35.2 ± 0.2 min, confirming the ultracompact binary nature of the system. The emission lines seen in SDSS J1730 are very narrow, although double-peaked, implying a low-inclination, face-on accretion disc; using the measured velocities of the line peaks, we estimate i ≤ 11°. This low inclination makes SDSS J1730 an excellent system for the identification of emission lines
Photoinduced anisotropic lattice dynamic response and domain formation in thermoelectric SnSe
Identifying and understanding the mechanisms behind strong phonon–phonon scattering in condensed matter systems is critical to maximizing the efficiency of thermoelectric devices. To date, the leading method to address this has been to meticulously survey the full phonon dispersion of the material in order to isolate modes with anomalously large linewidth and temperature-dependence. Here we combine quantitative MeV ultrafast electron diffraction (UED) analysis with Monte Carlo based dynamic diffraction simulation and first-principles calculations to directly unveil the soft, anharmonic lattice distortions of model thermoelectric material SnSe. A small single-crystal sample is photoexcited with ultrafast optical pulses and the soft, anharmonic lattice distortions are isolated using MeV-UED as those associated with long relaxation time and large displacements. We reveal that these modes have interlayer shear strain character, induced mainly by c-axis atomic displacements, resulting in domain formation in the transient state. These findings provide an innovative approach to identify mechanisms for ultralow and anisotropic thermal conductivity and a promising route to optimizing thermoelectric devices
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