250 research outputs found
Concentrating Photovoltaic Retrofit for Existing Parabolic Trough Solar Collectors: Design, Experiments, and Levelized Cost of Electricity
Photovoltaics and concentrating solar thermal power are two ways for generating electricity from sunlight, albeit through different methods. Parabolic trough style powerplants represent 3.6 GW of electricity production, but many of these plants are aging and being replaced with photovoltaics. An alternative option that could be employed to leverage the sunk capital cost associated with the primary optics would be the design of a pure photovoltaic retrofit working within the existing plant architecture. Here, a secondary optical concentrator is designed to use the existing primary optics of a parabolic trough type solar thermal powerplant. The design is a v-shaped secondary concentrator resulting in a predicted concentration ratio on a 20 mm wide target of 94. The concentrating photovoltaic receiver for retrofit of an RP-3 based parabolic trough has been constructed using multi-junction concentrator photovoltaic cells and experimentally demonstrated here for the first time. Calculated performance of the cells based on cell specifications should result in 31% efficiency at 85 °C. On-sun efficiencies were measured at an average value of 21% with operational temperatures between 55 and 120 °C. Levelized cost of electricity calculations predict the system to have the potential to be below 7¢/kWh based on predicted efficiencies and 13¢/kWh based on the measured values at cell costs of $5/cm2
Second-derivative spectrophotometry for the analysis of simvastatin in polymeric nanocapsules
Conventional spectrophotometry methods are very susceptible to the presence of interferences in complex mixtures such as nanoparticules, requiring prior treatment or extraction of the analyte, and not always providing an adequate response. Derivative spectrophotometry method is capable to eliminate its interference; it is an alternative method for drugs determination in complex matrices. This work investigated the utility of derivate spectrophotometry in assay of simvastatin in polymeric nanocapsules (SIVNC). Shimadzu® UV-1650 double-beam spectrophotometer with 1.0 cm quartz cells was used in this study. The second-order derivative spectrum was obtained employing Δλ=20,000 nm and scaling factor=9.0. The determinations were made at 239 nm (2D239) by zero-crossing method. 2D239 method was validated employing the parameters: specificity, linearity, robustness, precision and accuracy. Results: The specificity test showed there was no interference of constituents commonly found in SIVNC formulation in 2D239. The standard curve showed a correlation coefficient of 0.994. The robustness was evaluated by small changes in the conditions of sample analysis and however, no significant changes were observed regarding drug quantitation. The precision was demonstrated by relative standard deviation (RSD) of intra-day (RSD=1.61-3.76) and inter-day studies (RSD=2.32). The recovery test resulted in an average of 100.66%, which confirmed the accuracy of the method. The procedure was simple and rapid; therefore this technique offers an alternative for determination of SIVNC without interferences
Radial Velocities of Six OB Stars
We present new results from a radial velocity study of six bright OB stars
with little or no prior measurements. One of these, HD 45314, may be a
long-period binary, but the velocity variations of this Be star may be related
to changes in its circumstellar disk. Significant velocity variations were also
found for HD 60848 (possibly related to nonradial pulsations) and HD 61827
(related to wind variations). The other three targets, HD 46150, HD 54879, and
HD 206183, are constant velocity objects, but we note that HD 54879 has
H emission that may originate from a binary companion. We illustrate
the average red spectrum of each target.Comment: Accepted for publication in PASP July 2007 issu
The Long Period, Massive Binaries HD 37366 and HD 54662: Potential Targets for Long Baseline Optical Interferometry
We present the results from an optical spectroscopic analysis of the massive
stars HD 37366 and HD 54662. We find that HD 37366 is a double-lined
spectroscopic binary with a period of 31.8187 +/- 0.0004 days, and HD 54662 is
also a double lined binary with a much longer period of 557.8 +/- 0.3 days. The
primary of HD 37366 is classified as O9.5 V, and it contributes approximately
two-thirds of the optical flux. The less luminous secondary is a broad-lined,
early B-type main-sequence star. Tomographic reconstruction of the individual
spectra of HD 37366 reveals absorption lines present in each component,
enabling us to constrain the nature of the secondary and physical
characteristics of both stars. Tomographic reconstruction was not possible for
HD 54662; however, we do present mean spectra from our observations that show
that the secondary component is approximately half as bright as the primary.
The observed spectral energy distributions (SEDs) were fit with model SEDs and
galactic reddening curves to determine the angular sizes of the stars. By
assuming radii appropriate for their classifications, we determine distance
ranges of 1.4 - 1.9 and 1.2 - 1.5 kpc for HD 37366 and HD 54662, respectively.Comment: 27 pages, 8 figures, Accepted for publication in Ap
Social media for the dissemination of Cochrane child health evidence: evaluation study
© Michele P Dyson, Amanda S Newton, Kassi Shave, Robin M Featherstone, Denise Thomson, Aireen Wingert, Ricardo M Fernandes, Lisa Hartling. Originally published in the Journal of Medical Internet Research (http://www.jmir.org), 01.09.2017. This is an open-access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work, first published in the Journal of Medical Internet Research, is properly cited. The complete bibliographic information, a link to the original publication on http://www.jmir.org/, as well as this copyright and license information must be included.Background: Health care providers value ready access to reliable synthesized information to support point-of-care decision making. Web-based communities, facilitated by the adoption of social media tools such as Facebook, Twitter, and YouTube, are increasingly being used for knowledge dissemination, bridging the gap between knowledge generation and synthesis and knowledge implementation.
Objective: Our objective was to implement and evaluate a structured social media strategy, using multiple platforms, to disseminate Cochrane Child Health evidence to health care providers caring for children.
Methods: Our social media strategy had three components: daily "tweets" using the Cochrane Child Health Twitter account, weekly WordPress blog posts, and a monthly journal club on Twitter ("tweet chat"). Each tweet, blog, and journal club shared Cochrane evidence on a child health topic. We evaluated the strategy through (1) Twitter and blog site analytics, (2) traceable link (Bitly) statistics, (3) Altmetric.com scores for promoted evidence, and (4) participant feedback. We also tracked the resources required to write the blog, tweet content, and manage the strategy.
Results: The 22-week social media strategy ran between November 2014 and April 2015. We created 25 blog posts, sent 585 tweets, and hosted 3 tweet chats. Monthly blog visits and views and Twitter account followers increased over time. During the study period, the blog received 2555 visitors and 3967 page views from a geographically diverse audience of health care providers, academics, and health care organizations. In total, 183 traceable Bitly links received 3463 clicks, and the Twitter account gained 469 new followers. The most visited and viewed blog posts included gastrointestinal topics (lactose avoidance), research on respiratory conditions (honey for cough and treatments for asthma), and maternal newborn care (skin-to-skin contact). On Twitter, popular topics were related to public health (vaccination) and pain management. We collected Altmetric.com scores for 61 studies promoted during the study period and recorded an average increase of 11 points. Research staff (n=3) contributed approximately 433 hours to promotion activities and planning (6.5 hours each per week) to implement the social media strategy, and study investigators reviewed all content (blog posts and tweets).
Conclusions: This study provides empirical evidence on the use of a coordinated social media strategy for the dissemination of evidence to professionals providing health services to children and youth. The results and lessons learned from our study provide guidance for future knowledge dissemination activities using social media tools.This work was supported by Alberta Innovates—Health Solutions, grant number 201300653. LH and ASN are supported, in part, by Canadian Institutes of Health Research New Investigator Awards.info:eu-repo/semantics/publishedVersio
Wind Accretion and State Transitions in Cygnus X-1
We present the results of a spectroscopic monitoring program (from 1998 to
2002) of the H-alpha emission strength in HDE 226868, the optical counterpart
of the black hole binary, Cyg X-1. The H-alpha profiles consist of (1) a P
Cygni component associated with the wind of the supergiant, (2) emission
components that attain high velocity at the conjunctions and that probably form
in enhanced outflows both towards and away from the black hole, and (3) an
emission component that moves in anti-phase with the supergiant's motion. We
argue that the third component forms in accreted gas near the black hole, and
the radial velocity curve of the emission is consistent with a mass ratio of
M_X / M_opt = 0.36 +/- 0.05. We find that there is a general anti-correlation
between the H-alpha emission strength and X-ray flux in the sense that when the
H-alpha emission is strong (W_\lambda < -0.5 Angstroms) the X-ray flux is
weaker and the spectrum harder. On the other hand, there is no correlation
between H-alpha emission strength and X-ray flux when H-alpha is weak. During
the low/hard X-ray state, the strong wind is fast and the accretion rate is
relatively low, while in the high/soft state the weaker, highly ionized wind
attains only a moderate velocity and the accretion rate increases. We argue
that the X-ray transitions from the normal low/hard to the rare high/soft state
are triggered by episodes of decreased mass loss rate in the supergiant donor
star.Comment: 45 pages, 16 figures, ApJ, in pres
The N Enrichment and Supernova Ejection of the Runaway Microquasar LS 5039
We present an investigation of new optical and ultraviolet spectra of the
mass donor star in the massive X-ray binary LS 5039. The optical band spectral
line strengths indicate that the atmosphere is N-rich and C-poor, and we
classify the stellar spectrum as type ON6.5 V((f)). The N-strong and C-weak
pattern is also found in the stellar wind P Cygni lines of N V 1240 and C IV
1550. We suggest that the N-enrichment may result from internal mixing if the
O-star was born as a rapid rotator, or the O-star may have accreted N-rich gas
prior to a common-envelope interaction with the progenitor of the supernova. We
re-evaluated the orbital elements to find an orbital period of P=4.4267 +/-
0.0010 d. We compared the spectral line profiles with new non-LTE,
line-blanketed model spectra, from which we derive an effective temperature
T_eff = 37.5 +/- 1.7 kK, gravity log g = 4.0 +/- 0.1, and projected rotational
velocity V sin i = 140 +/- 8 km/s. We fit the UV, optical, and IR flux
distribution using a model spectrum and extinction law with parameters E(B-V)=
1.28 +/- 0.02 and R= 3.18 +/- 0.07. We confirm the co-variability of the
observed X-ray flux and stellar wind mass loss rate derived from the H-alpha
profile, which supports the wind accretion scenario for the X-ray production in
LS 5039. Wind accretion models indicate that the compact companion has a mass
M_X/M_sun = 1.4 +/- 0.4, consistent with its identification as a neutron star.
The observed eccentricity and runaway velocity of the binary can only be
reconciled if the neutron star received a modest kick velocity due to a slight
asymmetry in the supernova explosion (during which >5 solar masses was
ejected).Comment: 38 pages, 9 figures; 2004, ApJ, 600, Jan. 10 issue, in press
Discussion revised thanks to comments from P. Podsiadlowsk
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