481 research outputs found
Renewable build-up pathways for the US: Generation costs are not system costs
The transition to a future electricity system based primarily on wind and
solar PV is examined for all regions in the contiguous US. We present optimized
pathways for the build-up of wind and solar power for least backup energy needs
as well as for least cost obtained with a simplified, lightweight model based
on long-term high resolution weather-determined generation data. In the absence
of storage, the pathway which achieves the best match of generation and load,
thus resulting in the least backup energy requirements, generally favors a
combination of both technologies, with a wind/solar PV energy mix of about
80/20 in a fully renewable scenario. The least cost development is seen to
start with 100% of the technology with the lowest average generation costs
first, but with increasing renewable installations, economically unfavorable
excess generation pushes it toward the minimal backup pathway. Surplus
generation and the entailed costs can be reduced significantly by combining
wind and solar power, and/or absorbing excess generation, for example with
storage or transmission, or by coupling the electricity system to other energy
sectors.Comment: 11 pages, 6 figure
Holographic Complexity and Volume
The previously proposed "Complexity=Volume" or CV-duality is probed and
developed in several directions. We show that the apparent lack of universality
for large and small black holes is removed if the volume is measured in units
of the maximal time from the horizon to the "final slice" (times Planck area).
This also works for spinning black holes. We make use of the conserved "volume
current", associated with a foliation of spacetime by maximal volume surfaces,
whose flux measures their volume. This flux picture suggests that there is a
transfer of the complexity from the UV to the IR in holographic CFTs, which is
reminiscent of thermalization behavior deduced using holography. It also
naturally gives a second law for the complexity when applied at a black hole
horizon. We further establish a result supporting the conjecture that a
boundary foliation determines a bulk maximal foliation without gaps, establish
a global inequality on maximal volumes that can be used to deduce the
monotonicity of the complexification rate on a boost-invariant background, and
probe CV duality in the settings of multiple quenches, spinning black holes,
and Rindler-AdS.Comment: 39 pages, many figures; v2: minor edits, references adde
The Aquarius Co-Moving Group is Not a Disrupted Classical Globular Cluster
We present a detailed analysis of high-resolution, high S/N spectra for 5
Aquarius stream stars observed with the MIKE spectrograph on the Magellan Clay
telescope. Our sample represents one third of the 15 known members in the
stream. We find the stream is not mono-metallic: the metallicity ranges from
[Fe/H] = -0.63 to -1.58. No anti-correlation in Na-O abundances is present, and
we find a strong positive Mg-Al relationship, similar to that observed in the
thick disk. We find no evidence that the stream is a result of a disrupted
classical globular cluster, contrary to a previously published claim. High
[(Na, Ni, alpha)/Fe] and low [Ba/Y] abundance ratios in the stream suggests it
is not a tidal tail from a disrupted dwarf galaxy, either. The stream is
chemically indistinguishable from Milky Way field stars with the exception of
one candidate, C222531-145437. From its position, velocity, and detailed
chemical abundances, C222531-145437 is likely a star that was tidally disrupted
from omega-Centauri. We propose the Aquarius stream is Galactic in origin, and
could be the result from a disk-satellite perturbation in the Milky Way thick
disk on the order of a few Gyr ago: derived orbits, UVW velocities, and angular
momenta of the Aquarius members offer qualitative support for our hypothesis.
Assuming C222531-145437 is a tidally disrupted member of omega-Centauri, this
system is the most likely disk perturber. In the absence of compelling chemical
and/or dynamical evidence that the Aquarius stream is the tidal tail of a
disrupted satellite, we advocate the "Aquarius group" as a more appropriate
description. Like the Canis Major over-density, as well as the Hercules and
Monoceros groups, the Aquarius group joins the list of kinematically-identified
substructures that are not actually accreted material: they are simply part of
the rich complexity of the Milky Way structure.Comment: Accepted to MNRAS. Updated to journal versio
Making Anti-de Sitter Black Holes
It is known from the work of Banados et al. that a space-time with event
horizons (much like the Schwarzschild black hole) can be obtained from 2+1
dimensional anti-de Sitter space through a suitable identification of points.
We point out that this can be done in 3+1 dimensions as well. In this way we
obtain black holes with event horizons that are tori or Riemann surfaces of
genus higher than one. They can have either one or two asymptotic regions.
Locally, the space-time is isometric to anti-de Sitter space.Comment: LaTeX, 10 pages, 6 postscript figures, uses epsf.te
Superiority of Interferon-Free Regimens for Chronic Hepatitis C: The Effect on Health-Related Quality of Life and Work Productivity
Antivirals d’acció directa; Fatiga; Productivitat laboralAntivirales de acción directa; Fatiga; Productividad laboralDirect-acting antivirals; Fatigue; Work productivityPatient-reported outcomes (PROs) such as quality of life and work productivity are important for measuring patient's experience. We assessed PROs during and after treatment of hepatitis C virus (HCV) patients.
Data were obtained from a phase 3 open label study of sofosbuvir and ribavirin (SOF + RBV) with and without interferon (IFN). Patients completed 4 PRO assessment instruments (SF-36, Functional Assessment of Chronic Illness Therapy—Fatigue, Chronic Liver Disease Questionnaire— HCV, Work Productivity and Activity—Specific Health Problem) before, during, and after treatment.
A total of 533 patients with chronic HCV were enrolled; 28.9% treatment-naïve, 23.1% cirrhotic, 219 received IFN + SOF + RBV and 314 received IFN-free SOF + RBV. At baseline, there were no differences in PROs between the IFN-free and IFN-containing treatment arms (all P > 0.05). During treatment, patients receiving IFN + SOF + RBV had a substantial impairment in their PROs (up to −24.4% by treatment week 12, up to −8.3% at week 4 post-treatment). The PRO decrements seen in the SOF + RBV arm were smaller in magnitude (up to −7.1% by treatment week 12), and all returned to baseline or improved by post-treatment week 4. By 12 weeks after treatment cessation, patients who achieved sustained viral response-12 showed some improvement of PRO scores regardless of the regimen (up to +7.1%, P < 0.0001) or previous treatment experience. In multivariate analysis, the use of IFN was independently associated with lower PROs.
IFN-based regimens have a profoundly negative impact to PROs. By contrast, the impact of RBV on these PROs is relatively modest. Achieving HCV cure is associated with improvement of most of the PRO scores
Teaching Internationally, Learning Collaboratively: Intercultural Perspectives on Information Literacy and Metaliteracy (IPILM)
Intercultural Perspectives on Information Literacy and Metaliteracy (IPILM) is a discourse- oriented learning environment that engages students from diverse cultural backgrounds to participate in collaborative knowledge construction. The objective is to evolve a thematic approach to course design that includes elements of open pedagogy, information literacy, and metaliteracy. IPILM invites participation from educators and learners from around the world and has witnessed an increase in participating countries. This paper describes the concept of IPILM and demonstrates the implementation of this approach in practice. The initiative was well received by students and is both feasible and sustainable as an intercultural learning endeavor. IPILM is an ongoing project and a work in progress that is an adaptable model which may be transferred to disparate fields of teaching and learning or adopted by international communities of instructors
Translation and manipulation of silicon nanomembranes using holographic optical tweezers
We demonstrate the use of holographic optical tweezers for trapping and manipulating silicon nanomembranes. These macroscopic free-standing sheets of single-crystalline silicon are attractive for use in next-generation flexible electronics. We achieve three-dimensional control by attaching a functionalized silica bead to the silicon surface, enabling non-contact trapping and manipulation of planar structures with high aspect ratios (high lateral size to thickness). Using as few as one trap and trapping powers as low as several hundred milliwatts, silicon nanomembranes can be rotated and translated in a solution over large distances
High-Resolution Spectroscopic Study of Extremely Metal-Poor Star Candidates from the SkyMapper Survey
The SkyMapper Southern Sky Survey is carrying out a search for the most
metal-poor stars in the Galaxy. It identifies candidates by way of its unique
filter set that allows for estimation of stellar atmospheric parameters. The
set includes a narrow filter centered on the Ca II K 3933A line, enabling a
robust estimate of stellar metallicity. Promising candidates are then confirmed
with spectroscopy. We present the analysis of Magellan-MIKE high-resolution
spectroscopy of 122 metal-poor stars found by SkyMapper in the first two years
of commissioning observations. 41 stars have [Fe/H] <= -3.0. Nine have [Fe/H]
<= -3.5, with three at [Fe/H] ~ -4. A 1D LTE abundance analysis of the elements
Li, C, Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Co, Ni, Zn, Sr, Ba and Eu shows
these stars have [X/Fe] ratios typical of other halo stars. One star with low
[X/Fe]
[X/Fe values appears to be "Fe-enhanced," while another star has an extremely
large [Sr/Ba] ratio: >2. Only one other star is known to have a comparable
value. Seven stars are "CEMP-no" stars ([C/Fe] > 0.7, [Ba/Fe] < 0). 21 stars
exhibit mild r-process element enhancements (0.3 <=[Eu/Fe] < 1.0), while four
stars have [Eu/Fe] >= 1.0. These results demonstrate the ability to identify
extremely metal-poor stars from SkyMapper photometry, pointing to increased
sample sizes and a better characterization of the metal-poor tail of the halo
metallicity distribution function in the future.Comment: Minor corrections to text, missing data added to Tables 3 and 4;
updated to match published version. Complete tables included in sourc
- …