We study quasi-periodic pulsations (QPPs) in the SOL2014-09-10 event that was detected by the
Geostationary Operational Environmental Satellites
(GOES), the
Atmospheric Imaging Assembly
(AIA) and the
...Extreme Ultraviolet Variability Experiment
(EVE) onboard the
Solar Dynamics Observatory
(SDO), and the
Gamma Ray Burst Monitor
(GBM) onboard the
Fermi
satellite. Previous studies have found that this flare displays four-minute QPPs in a broad range of wavelengths. In this article, we find that this event also shows QPPs with a period of around one minute. Using the Fast Fourier Transform (FFT) method, the light curves are decomposed into fast- and slowly varying components with a separation at
≈
100
seconds
. The four-minute QPPs are in the slowly varying component, and the one-minute QPPs are identified with the fast-varying components in the impulsive and maximum phases. Similarly as the four-minute QPPs, the one-minute QPPs are simultaneously found in soft X-rays (SXR), extreme ultraviolet (EUV), and hard X-ray (HXR) emission. High correlations are found between the fast-varying components at the different wavelengths, especially between SXR and HXR. The spatial location of the sources of one-minute QPPs differ from those of the four-minute QPPs. The four-minute QPPs appear in the whole flare region, while the one-minute QPPs tend to originate from the flare loop footpoints. This finding provides an observational constraint for the physical origin of the QPPs.
Summary
The aim of the current study was to use a Bayesian network meta-analysis to evaluate the relative benefits and risks of balloon kyphoplasty (BK), percutaneous vertebroplasty (PVP), and ...non-surgical treatment (NST) for patients with osteoporotic vertebral compression fractures (OVCFs). The results demonstrate that for pain and functional status, PVP was significantly better than NST, while the three treatments did not significantly differ in other outcomes.
Introduction
BK, PVP, and NST are widely used to treat OVCFs, but preferable treatment is unknown. The aim of the current study was to use a Bayesian network meta-analysis to evaluate the relative benefits and risks of BK, PVP, and NST for patients with OVCFs.
Methods
PubMed, EMBASE, and the Cochrane Library were screened. Based on the preplanned eligibility criteria, we screened and included randomized controlled trials that compared BK, PVP, and NST in treating patients with OVCFs. The risk of bias for individual studies was appraised. The data were pooled using a Bayesian network meta-analysis and a traditional direct comparison meta-analysis.
Results
Of the 1057 relevant studies, 15 were eligible and included. Compared with NST, PVP significantly reduced pain, Oswestry Disability Index (ODI), and Roland–Morris Disability Questionnaire (RMDQ). The comparative efficacy of BK and PVP was similar for pain (mean difference (MD) 0.51, 95% credible interval (CrI) − 0.35 to 1.4), ODI (MD 0.11, 95% CrI − 13 to 13), and RMDQ (MD 1.2, 95% CrI − 2.7 to 5.4). The European Quality of Life–5 Dimensions (EQ–5D) and Physical Component Summary subscales of the Medical Outcomes Study 36-Item Short-Form General Health Survey (SF-36 PCS) did not differ significantly. There were also no substantial differences in the risks of subsequent vertebral fractures, adjacent vertebral fractures, and re-fractures at the treated level across all comparators. The results of pairwise meta-analyses were almost consistent with those of network meta-analyses. The treatment ranking indicated that PVP had the highest probability of being the most effective for pain, ODI, RMDQ, and EQ-5D. BK had the highest probability of improving SF-36 PCS and of reducing the risk of subsequent vertebral fractures and re-fractures at the treated level. NST was ranked first in preventing adjacent vertebral fractures.
Conclusion
PVP was the most effective method for improving pain, functional status, and quality of life (based on EQ-5D). BK emerged as the best intervention for decreasing the risk of subsequent vertebral fractures and re-fractures at the treated level. NST could be ranked first in reducing adjacent vertebral fractures. The future directions of OVCFs treatment will depend on the outcomes of additional and larger randomized trials in comparing BK with PVP.
ABSTRACT In this paper, we report our multiwavelength observations of the C3.1 circular-ribbon flare SOL2015-10-16T10:20 in active region (AR) 12434. The flare consisted of a circular flare ribbon ...(CFR), an inner flare ribbon (IFR) inside it, and a pair of short parallel flare ribbons (PFRs). The PFRs located to the north of the IFR were most striking in the Interface Region Imaging Spectrograph (IRIS) 1400 and 2796 images. For the first time, we observed the circular-ribbon flare in the Ca ii H line of the Solar Optical Telescope on board Hinode, which has a similar shape as observed in the Atmospheric Imaging Assembly 1600 on board the Solar Dynamic Observatory (SDO). Photospheric line-of-sight magnetograms from the Helioseismic and Magnetic Imager on board SDO show that the flare is associated with positive polarities with a negative polarity inside. The IFR and CFR were cospatial with the negative polarity and positive polarities, implying the existence of a magnetic null point ( ) and a dome-like spine-fan topology. During the impulsive phase of the flare, "two-step" raster observations of IRIS with a cadence of 6 s and an exposure time of 2 s showed plasma downflow at the CFR in the Si iv λ1402.77 line ( ), suggesting chromospheric condensation. The downflow speeds first increased rapidly from a few km s−1 to the peak values of 45-52 km s−1, before decreasing gradually to the initial levels. The decay timescales of condensation were 3-4 minutes, indicating ongoing magnetic reconnection. Interestingly, the downflow speeds are positively correlated with the logarithm of the Si iv line intensity and time derivative of the GOES soft X-ray (SXR) flux in 1-8 . The radio dynamic spectra are characterized by a type III radio burst associated with the flare, which implies that the chromospheric condensation was most probably driven by nonthermal electrons. Using an analytical expression and the peak Doppler velocity, we derive the lower limit of energy flux of the precipitating electrons, i.e., 0.65 × 1010 erg cm−2 s−1. The Si iv line intensity and SXR derivative show quasi-periodic pulsations with periods of 32-42 s, which are likely caused by intermittent null-point magnetic reconnections modulated by the fast wave propagating along the fan surface loops at a phase speed of 950-1250 km s−1. Periodic accelerations and precipitations of the electrons result in periodic heating observed in the Si iv line and SXR.
The present study is aimed to investigate and compare effects of biodiesel-ethanol (BE) and biodiesel-n-butanol (BBu) blends on combustion, performance and emissions of a direct-injection diesel ...engine. Experiments were conducted on BE5 (5% ethanol and 95% biodiesel, v/v), BE10, BE15, BBu5, BBu10 and BBu15, at five engine loads and at 1800 rpm. In regard to combustion characteristics, effects on maximum heat release rate, maximum in-cylinder pressure, start of combustion, combustion duration and coefficients of variations (COVs) of IMEP and maximum increase rate of in-cylinder pressure were investigated. In regard to engine performance, effects on BSFC and BTE were investigated. The blended fuels have adverse effects on engine performance especially at low load, with the BE blends having more adverse effects than the BBu blends. Moreover, on average of the five engine loads, the BBu and BE blends increase CO emission by 13.7% and 22.8% and HC emission by 5.6% and 29.2%, respectively; but reduce NOx emission by 6.5% and 28.0%, particle mass concentration by 20.7% and 20.6% and particle number concentration by 22% and 21%, respectively. Overall, the BE blends are more effective in reducing particulate and NOx emissions but the BBu blends would lead to less increase in CO and HC emissions.
•BBu blends have less adverse influence on BSFC and BTE than BE blends.•BE/BBu blends have adverse effects on combustion noise and stability of power output.•BE blends are better than BBu blends in reducing NOX and PM emissions.•BE blends lead to higher CO and HC emissions than BBu blends.
Miniaturization has been an everlasting theme in the development of semiconductor lasers. One important breakthrough in this process in recent years is the use of metal-dielectric composite ...structures that made truly subwavelength lasers possible. Many different designs of metallic cavity semiconductor nanolasers have been proposed and demonstrated. In this article, we will review some of the most exciting progresses in this newly emerging field. In particular, we will focus on metallic-cavity nanolasers with volume smaller than wavelength cubed under electrical injection with emphasis on high-temperature operation. Such devices will serve as an important component in the future integrated nanophotonic systems due to its ultra-small size.
In this paper, we report our multiwavelength observations of the simultaneous transverse and longitudinal oscillations in a quiescent prominence. The prominence was observed by the Global Oscillation ...Network Group and by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory on 2015 June 29. A GOES C2.4 flare took place in NOAA active region 12373, which was associated with a pair of short ribbons and a remote ribbon. During the impulsive phase of the flare, a coronal jet spurted out of the primary flare site and propagated in the northwest direction at an apparent speed of ∼224 km s−1. Part of the jet stopped near the remote ribbon. The remaining part continued moving forward before stopping to the east of the prominence. Once the jet encountered the prominence, it pushed the prominence to oscillate periodically. The transverse oscillation of the eastern part (EP) of prominence can be divided into two phases. In phase I, the initial amplitude, velocity, period, and damping timescale are ∼4.5 Mm, ∼20 km s−1, ∼25 minutes, and ∼7.5 hr, respectively. The oscillation lasted for two cycles. In phase II, the initial amplitude increases to ∼11.3 Mm, while the initial velocity halves to ∼10 km s−1. The period increases by a factor of ∼3.5. With a damping timescale of ∼4.4 hr, the oscillation lasted for about three cycles. The western part of prominence also experienced transverse oscillation. The initial amplitude is only ∼2 Mm and the velocity is less than 10 km s−1. The period (∼27 minutes) is slightly longer than that of the EP in phase I. The oscillation lasted for about four cycles with the shortest damping timescale (∼1.7 hr). To the east of prominence, a handful of horizontal threads experienced longitudinal oscillation. The initial amplitude, velocity, period, and damping timescale are ∼52 Mm, ∼50 km s−1, ∼99 minutes, and 2.5 hr, respectively. To our knowledge, this is the first report of simultaneous transverse and longitudinal prominence oscillations triggered by a coronal jet.
A new series of starburst triarylamine fluorophores SBCHO, DBCHO, CZCHO, CZCN, and SBCN, that incorporate diphenylamine or carbazole as the electron donor and dicyanovinyl or aldehyde as the electron ...acceptor, has been prepared and their photophysical properties are investigated. In sharp contrast to most red-emitting dopants, which show serious aggregation-caused quench phenomena, the new starburst triphenylamine derivatives reported here show unique enhanced emission in the solid state or upon aggregation. Organic light emitting diodes using these compounds as non-doped host emitters and hole transporters have been fabricated. The highest external quantum yield reaches 2.09% for CZCHO. SBCHO was investigated as a chlorine gas fluorescence (FL) solid-film sensor for the first time. The high-intensity emission was turned off' immediately after being blown by Cl2 gas.
ABSTRACT We explore the quasi-periodic pulsations (QPPs) in a solar flare observed by Fermi Gamma-ray Burst Monitor, Solar Dynamics Observatory, Solar Terrestrial Relations Observatory, and Interface ...Region Imaging Spectrograph (IRIS) on 2014 September 10. QPPs are identified as the regular and periodic peaks on the rapidly varying components, which are the light curves after removing the slowly varying components. The QPPs display only three peaks at the beginning on the hard X-ray emissions, but 10 peaks on the chromospheric and coronal line emissions, and more than seven peaks (each peak corresponds to a type III burst on the dynamic spectra) at the radio emissions. A uniform quasi-period of about 4 minutes is detected among them. AIA imaging observations exhibit that the 4-minute QPPs originate from the flare ribbon and tend to appear on the ribbon front. IRIS spectral observations show that each peak of the QPPs tends to a broad line width and a red Doppler velocity at C i, O iv, Si iv, and Fe xxi lines. Our findings indicate that the QPPs are produced by the non-thermal electrons that are accelerated by the induced quasi-periodic magnetic reconnections in this flare.
Semiconductor alloy nanowires with spatially graded compositions (and bandgaps) provide a new material platform for many new multifunctional optoelectronic devices, such as broadly tunable lasers, ...multispectral photodetectors, broad‐band light emitting diodes (LEDs) and high‐efficiency solar cells. In this review, we will summarize the recent progress on composition graded semiconductor alloy nanowires with bandgaps graded in a wide range. Depending on different growth methods and material systems, two typical nanowire composition grading approaches will be presented in detail, including composition graded alloy nanowires along a single substrate and those along single nanowires. Furthermore, selected examples of applications of these composition graded semiconductor nanowires will be presented and discussed, including tunable nanolasers, multi‐terminal on‐nanowire photodetectors, full‐spectrum solar cells, and white‐light LEDs. Finally, we will make some concluding remarks with future perspectives including opportunities and challenges in this research area.
Semiconductor alloy nanowires with spatially graded compositions (and bandgaps) provide a new material platform for many new multifunctional optoelectronic devices, such as broadly tunable lasers, multispectral photodetectors, broad‐band light emitting diodes (LEDs) and high‐efficiency solar cells. Here, recent studies on composition or bandgap‐graded semiconductor alloy nanowires based on a single substrate or along single nanowires are reviewed.
Through repeated interactions, firms today refine their understanding of individual users’ preferences adaptively for personalization. In this paper, we use a continuous-time bandit model to analyze ...firms that recommend content to multihoming consumers, a representative setting for strategic learning of consumer preferences to maximize lifetime value. In both monopoly and duopoly settings, we compare a forward-looking recommendation algorithm that balances exploration and exploitation to a myopic algorithm that only maximizes the quality of the next recommendation. Our analysis shows that, compared with a monopoly, firms competing for users’ attention focus more on exploitation than exploration. When users are impatient, competition decreases the return from developing a forward-looking algorithm. In contrast, development of a forward-looking algorithm may hurt users under monopoly but always benefits users under competition. Competing firms’ decisions to invest in a forward-looking algorithm can create a prisoner’s dilemma. Our results have implications for artificial intelligence adoption and for policy makers on the effect of market power on innovation and consumer welfare.
This paper was accepted by Dmitri Kuksov, marketing.
Supplemental Material:
The online appendix is available at
https://doi.org/10.1287/mnsc.2023.4722
.
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