Double Peak Type Research Articles

The double-peaked type I X-ray bursts with different mass accretion rate and fuel composition

ABSTRACT Using the mesa (Modules for Experiments in Stellar Astrophysics) code, we have carried out a detailed survey of the available parameter space for the double-peaked type I X-ray bursts. We find that the double-peaked structure appears at mass accretion rate $\dot{M}$ in the range of $\sim (4-8)\times 10^{-10}\, {\rm M}_{\odot }\,{\rm yr}^{-1}$ when metallicity Z = 0.01, while in the range of $\sim (4-8)\times 10^{-9}\, {\rm M}_{\odot }\,\rm {yr}^{-1}$ when Z = 0.05. Calculations of the metallicity impact suggest that the double peaks will disappear when Z ≲ 0.005 for $\dot{M}=5\times 10^{-10}\, {\rm M}_{\odot }\,\rm {yr}^{-1}$ and Z ≲ 0.04 for $\dot{M}=5\times 10^{-9}\, {\rm M}_{\odot }\,\rm {yr}^{-1}$. Besides, the impacts of base heating Qb, as well as nuclear reaction waiting points: $^{22}\rm {Mg}$, $^{26}\rm {Si}$, $^{30}\rm {S}$, $^{34}\rm {Ar}$, 56Ni, $^{60}\rm Zn$, $^{64}\rm {Ge}$, $^{68}\rm {Se}$, and $^{72}\rm {Kr}$ have been explored. The luminosity of the two peaks decreases as Qb increases. 68Se(p, γ)69Br is the most sensitive reaction, the double peaks disappear assuming that 56Ni(p, γ)57Cu, and 64Ge(p, γ)65As reaction rates have been underestimated by a factor of 100 and the 22Mg(α, p)25Al reaction rate has been overestimated by a factor of 100, which indicates that 22Mg, 56Ni, 64Ge, and 68Se are possibly the most important nuclear waiting points impedance in the thermonuclear reaction flow to explain the double-peaked bursts. Comparisons to the double-peaked bursts from 4U 1636−53 and 4U 1730−22 suggest that the nuclear origins of double-peaked type I X-ray bursts are difficult to explain the observed larger peak times ($t_{\rm p,1}\gtrsim 4\, {\rm s}$, $t_{\rm p,2}\gtrsim 8\, {\rm s}$) and smaller peak ratio (r1, 2 ≲ 0.5). The composition of ashes from double-peaked bursts is very different from the single-peaked bursts especially for the heavier p-nuclei.

Comprehensive Study on Microscopic Pore Structure and Displacement Mechanism of Tight Sandstone Reservoirs: A Case Study of the Chang 3 Member in the Weibei Oilfield, Ordos Basin, China

With the continuous growth in global energy demand, research and development of unconventional oil and gas reservoirs have become crucial in the field of energy. This study focuses on the Chang 3 reservoir of the Yanchang Formation in the Ordos Basin, Weibei Oilfield, China. This reservoir is a typical tight sandstone reservoir, and its microscopic pore structure and displacement mechanism are essential for the efficient development of tight oil. However, the reservoir faces challenges such as complex microscopic pore structures and unclear displacement mechanisms, which hinder the efficient development of tight oil. In light of these challenges, through various studies including core observation, high-pressure mercury injection tests, water flooding experiments, oil-water two-phase relative permeability measurements, and stress sensitivity experiments, it was found that the Chang 3 reservoir exhibits strong microscopic heterogeneity. The pore-throat distribution characteristics mainly present two types: single peak and double peak, with the double peak type being predominant. The reservoir was classified and evaluated based on these characteristics. The improved injection ratio and properties enhance oil displacement efficiency, but an increase in irreducible water saturation has a negative impact on efficiency. The stress sensitivity of the reservoir fluctuates between weak and strong, with permeability being sensitive to net confining pressure. It is recommended to pay particular attention to the stress-sensitivity characteristics during reservoir development. The research results provide a scientific basis for the optimized development of tight oil reservoirs in this region, promote the sustainable development of unconventional oil and gas resources, and have significant theoretical and practical implications.

The Effects of Thomson Scattering and Chemical Mixing on Early-time Light Curves of Double-peaked Type IIb Supernovae

Previous numerical simulations of double-peaked Type IIb supernova (SN IIb) light curves have demonstrated that the radius and mass of the hydrogen-rich envelope of the progenitor star can significantly influence the brightness and timescale of the early-time light curve around the first peak. In this study, we investigate how Thomson scattering and chemical mixing in the SN ejecta affect the optical light curves during the early stages of the SNe IIb using radiation hydrodynamics simulations. By comparing the results from two different numerical codes (i.e., STELLA and SNEC), we find that the optical brightness of the first peak can be reduced by more than a factor of 3 as a result of the effect of Thomson scattering that causes the thermalization depth to be located below the Rosseland mean photosphere, compared to the corresponding case where this effect is ignored. We also observe a short-lived plateau-like feature lasting for a few days in the early-time optical light curves of our models, in contrast to typical observed SNe IIb that show a quasi-linear decrease in optical magnitudes after the first peak. A significant degree of chemical mixing between the hydrogen-rich envelope and the helium core in SN ejecta is required to reconcile this discrepancy between the model prediction and observation. Meanwhile, to properly reproduce the first peak, a significant mixing of 56Ni into the hydrogen-rich outermost layers should be restricted. Our findings indicate that inferring the SN IIb progenitor structure from a simplified approach that ignores these two factors may introduce substantial uncertainty.

SN 2020bio: A Double-peaked, H-poor Type IIb Supernova with Evidence of Circumstellar Interaction

We present photometric and spectroscopic observations of SN 2020bio, a double-peaked Type IIb supernova (SN) discovered within a day of explosion, primarily obtained by Las Cumbres Observatory and Swift. SN 2020bio displays a rapid and long-lasting initial decline throughout the first week of its light curve, similarly to other well-studied Type IIb SNe. This early-time emission is thought to originate from the cooling of the extended outer hydrogen-rich (H-rich) envelope of the progenitor star that is shock heated by the SN explosion. We compare SN 2020bio to a sample of other double-peaked Type IIb SNe in order to investigate its progenitor properties. Analytical model fits to the early-time emission give progenitor radius (≈100–1500 R ⊙) and H-rich envelope mass (≈0.01–0.5 M ⊙) estimates that are consistent with other Type IIb SNe. However, SN 2020bio displays several peculiarities, including (1) weak H spectral features indicating a greater amount of mass loss than other Type IIb progenitors; (2) an underluminous secondary light-curve peak that implies a small amount of synthesized 56Ni (M Ni ≈0.02 M ⊙); and (3) low-luminosity nebular [O i] and interaction-powered nebular features. These observations are more consistent with a lower-mass progenitor (M ZAMS ≈ 12 M ⊙) that was stripped of most of its H-rich envelope before exploding. This study adds to the growing diversity in the observed properties of Type IIb SNe and their progenitors.

Spatiotemporal Assessment of Atmospheric Pollutants in Yancheng City, Eastern Coastal City of China

Atmospheric environmental pollution has become a critical issue in eastern coastal cities in China, so a broad understanding of its spatiotemporal characteristics is of importance to develop public policies. In this study, hourly data of ρ(PM2.5), ρ(PM10), ρ(NO2), ρ(SO2), ρ(O3) and φ(CO) of five different types of national air quality monitoring sites from 2016 to 2020 were analyzed, combined with the change of meteorological elements in the same period in Yancheng, which was a rapidly developed eastern coastal city in China. The results indicated that the pollutant concentrations except for ρ(O3) was low in summer and high in winter, decreasing year by year from 2016 to 2020. The proportion of moderately and heavily contaminated days in the whole year was decreasing from 80 days in 2016 to 52 days in 2020, and the days with good quality increased from 284 days in 2016 to 311 days in 2020. ρ(O3) was the highest in spring and the lowest in winter, increasing slightly year by year. The variation of ρ(PM2.5), ρ(PM10), ρ(NO2), ρ(SO2) and φ(CO) showed a double-peak type, reaching the peak value at 8:00–10:00 and 20:00–22:00, corresponding to the early and evening rush hours. ρ(PM2.5), ρ(PM10) and φ(CO) on the weekend were higher than on weekdays, while an insignificant difference of ρ(NO2), ρ(O3) and ρ(SO2) was found between weekdays and the weekend. Wind direction played a key role in the variation of pollutant concentration in the Yancheng urban area, and the correlation analysis indicated that ρ(PM2.5) and ρ(PM10) were highly correlated to wind direction. Temperature was positively correlated to ρ(O3), while air pressure was significantly negatively correlated to ρ(O3). Relative humidity was negatively correlated to ρ(PM2.5), ρ(PM10), ρ(NO2), ρ(SO2) and φ(CO), while air pressure was positively correlated with these pollutants.

Revealing the Progenitor of SN 2021zby through Analysis of the TESS Shock-cooling Light Curve

We present early observations and analysis of the double-peaked Type IIb supernova (SN IIb) SN 2021zby. TESS captured the prominent early shock-cooling peak of SN 2021zby within the first ∼10 days after explosion with a 30 minute cadence. We present optical and near-infrared spectral series of SN 2021zby, including three spectra during the shock-cooling phase. Using a multiband model fit, we find that the inferred properties of its progenitor are consistent with a red supergiant or yellow supergiant, with an envelope mass of ∼0.30–0.65 M ⊙ and an envelope radius of ∼120–300 R ⊙. These inferred progenitor properties are similar to those of other SNe IIb with a double-peaked feature, such as SNe 1993J, 2011dh, 2016gkg, and 2017jgh. This study further validates the importance of the high cadence and early coverage in resolving the shape of the shock-cooling light curve, while the multiband observations, particularly UV, are also necessary to fully constrain the progenitor properties.

Return of 4U 1730–22 after 49 yr Silence: The Peculiar Burst Properties of the 2021/2022 Outbursts Observed by Insight-HXMT

Staying in quiescence for 49 yr, 4U 1730–22 became active and had two outbursts in 2021 and 2022; 10 thermonuclear X-ray bursts were detected with Insight-HXMT. Among them, the faintest burst showed a double-peaked profile, placing the source as the seventh accreting neutron star (NS) exhibiting double-peaked type I X-ray bursts; the other bursts showed photospheric radius expansion (PRE). The properties of a double-peaked non-PRE burst indicate that it could be related to a stalled burning front. For the five bright PRE bursts, apart from the emission from the neutron star (NS) surface, we find the residuals both in the soft (<3 keV) and hard (>10 keV) X-ray bands. Time-resolved spectroscopy reveals that the excess can be attributed to an enhanced preburst/persistent emission or the Comptonization of the burst emission by the corona. We find, the burst emission shows a rise until the photosphere touches down to the NS surface rather than the theoretical predicted constant Eddington luminosity. The shortage of the burst emission in the early rising phase is beyond the occlusion by the disk. We speculate that the findings above are due to that the obscured part (not only the lower part) of the NS surface is exposed to the line of sight due to the evaporation of the obscured material by the burst emission, or the burst emission is anisotropic (ξ > 1) in the burst early phase. In addition, based on the fluxes of PRE bursts at their touchdown times, we derive a distance estimation as 9.0–12.4 kpc.

The Luminous and Double-peaked Type Ic Supernova 2019stc: Evidence for Multiple Energy Sources

Abstract We present optical photometry and spectroscopy of SN 2019stc (=ZTF19acbonaa), an unusual Type Ic supernova (SN Ic) at a redshift of z = 0.117. SN 2019stc exhibits a broad double-peaked light curve, with the first peak having an absolute magnitude of M r = −20.0 mag, and the second peak, about 80 rest-frame days later, M r = −19.2 mag. The total radiated energy is large, E rad ≈ 2.5 × 1050 erg. Despite its large luminosity, approaching those of Type I superluminous supernovae (SLSNe), SN 2019stc exhibits a typical SN Ic spectrum, bridging the gap between SLSNe and SNe Ic. The spectra indicate the presence of Fe-peak elements, but modeling of the first light-curve peak with radioactive heating alone leads to an unusually high nickel mass fraction of f Ni ≈ 0.31 (M Ni ≈ 3.2 M ⊙). Instead, if we model the first peak with a combined magnetar spin-down and radioactive heating model we find a better match with M ej ≈ 4 M ⊙, a magnetar spin period of P spin ≈ 7.2 ms, and magnetic field of B ≈ 1014 G, and f Ni ≲ 0.2 (consistent with SNe Ic). The prominent second peak cannot be naturally accommodated with radioactive heating or magnetar spin-down, but instead can be explained as circumstellar interaction with ≈0.7 M ⊙ of hydrogen-free material located ≈400 au from the progenitor. Accounting for the ejecta mass, circumstellar shell mass, and remnant neutron star mass, we infer a CO core mass prior to explosion of ≈6.5 M ⊙. The host galaxy has a metallicity of ≈0.26 Z ⊙, low for SNe Ic but consistent with SLSNe. Overall, we find that SN 2019stc is a transition object between normal SNe Ic and SLSNe.

The double-peaked Type Ic supernova 2019cad: another SN 2005bf-like object

ABSTRACT We present the photometric and spectroscopic evolution of supernova (SN) 2019cad during the first ∼100 d from explosion. Based on the light-curve morphology, we find that SN 2019cad resembles the double-peaked Type Ib/c SN 2005bf and the Type Ic PTF11mnb. Unlike those two objects, SN 2019cad also shows the initial peak in the redder bands. Inspection of the g-band light curve indicates the initial peak is reached in ∼8 d, while the r-band peak occurred ∼15 d post-explosion. A second and more prominent peak is reached in all bands at ∼45 d past explosion, followed by a fast decline from ∼60 d. During the first 30 d, the spectra of SN 2019cad show the typical features of a Type Ic SN, however, after 40 d, a blue continuum with prominent lines of Si ii λ6355 and C ii λ6580 is observed again. Comparing the bolometric light curve to hydrodynamical models, we find that SN 2019cad is consistent with a pre-SN mass of 11 M⊙, and an explosion energy of 3.5 × 1051 erg. The light-curve morphology can be reproduced either by a double-peaked 56Ni distribution with an external component of 0.041 M⊙, and an internal component of 0.3 M⊙ or a double-peaked 56Ni distribution plus magnetar model (P ∼ 11 ms and B ∼ 26 × 1014 G). If SN 2019cad were to suffer from significant host reddening (which cannot be ruled out), the 56Ni model would require extreme values, while the magnetar model would still be feasible.

Magnetar-driven Shock Breakout Revisited and Implications for Double-peaked Type I Superluminous Supernovae

Abstract The discovery of early bumps in some type-I superluminous supernovae (SLSNe-I) before the main peaks offers an important clue to their energy source mechanisms. In this paper, we updated an analytic magnetar-powered model for fitting the multiband light curves of double-peaked SLSNe-I. The early bump is powered by magnetar-driven shock-breakout thermal emission, and the main peak is powered by a radiative diffusion through the supernova (SN) ejecta as in the standard magnetar-powered model. Generally, the diffusive luminosity is greater than the shock-breakout luminosity at the early time, which usually makes the shock-breakout bumps unclear to observe. To obtain a clear double-peaked light curve, inefficient magnetar heating at early times is required. This model is applied to three well-observed double-peaked SLSNe-I (i.e., SN2006oz, LSQ14bdq, and DES14Xtaz). We find that a relatively massive SN ejecta with M ej ≃ 10.2–18.1M ⊙ and relatively large kinetic energy of SN ejecta erg are required, and the thermalization efficiency of the magnetar heating is suppressed before t delay, which is in the range of ≃15–43 days. The model can reproduce the observed light curves well, with a reasonable and similar set of physical parameters for both the early bump and the main peak, strengthening support for the magnetar-powered model. In the future, modeling of the double-peaked SLSNe-I will become more feasible as more events are discovered before the early bump.

The Effect of Circumstellar Matter on the Double-peaked Type Ic Supernovae and Implications for LSQ14efd, iPTF15dtg, and SN 2020bvc

Abstract Double-peaked light curves are observed for some Type Ic supernovae (SNe Ic), including LSQ14efd, iPTF15dtg, and SN 2020bvc. One possible explanation of the first peak would be shock-cooling emission from massive extended material around the progenitor, which is produced by mass eruption or rapid expansion of the outermost layers of the progenitor shortly before the supernova explosion. We investigate the effects of such circumstellar matter (CSM) on the multiband optical light curves of SNe Ic using the radiation hydrodynamics code STELLA. Two different SNe Ic progenitor masses at the pre-SN stage (3.93 M ⊙ and 8.26 M ⊙) are considered in the SN models. The adopted parameter space consists of the CSM mass of M CSM = 0.05–0.3M ⊙, the CSM radius of R CSM = 1013–1015 cm, and the explosion energy of E burst = (1.0–12.0) × 1051 erg. We also investigate the effects of the radioactive nickel distribution on the overall shape of the light curve and the color evolution. Comparison of our SN models with the double-peaked SNe Ic LSQ14efd, iPTF15dtg, and SN 2020bvc indicates that these three SNe Ic had a similar CSM structure (i.e., M CSM ≈ 0.1–0.2M ⊙ and R CSM = 1013–1014 cm), which might imply a common mechanism for their CSM formation. The implied mass-loss rate of M ̇ ≳ 1.0 M ⊙ yr − 1 is too high to be explained by the previously suggested scenarios for pre-SN eruption, which calls for a novel mechanism.

Human papillomavirus infection rate, distribution characteristics, and risk of age in pre- and postmenopausal women

BackgroundThe incidence rate of cervical cancer is increasing yearly. The persistent infection of high-risk human papillomavirus (HPV) is the main factor leading to cervical cancer. HPV infection is double peak type. This study aimed at analyzing the HPV distribution characteristics, infection rate, and risk of age in pre- and postmenopausal women. So as to provide reference for the prevention of HPV infection and cervical cancer screening strategy.MethodsA retrospective analysis of 4614 women who underwent cervical cytology, and HPV examination from January 2018 to October 2019 at the healthcare department of Wuhan Union Hospital was done. We explored the characteristics and distribution of HPV infections around the menopause, then comparing the infection rate of HPV in postmenopause and over 65 years old, in order to analyze the influence of different ages on HPV infection.ResultsGenerally, the HPV infection rate was 13.10% (539/4115), whereby the high-risk subtype constituted 73.84% (398/539) of all positive cases. On the other hand, the HPV39 infection was more common in postmenopausal women; however, there was no significant difference in the distribution of the other types in the pre- and postmenopausal women. The first four types were 52/53/58/16. The results further showed that the rates of HPV infection before and after menopause were 12.34% (367/2975) and 15.09% (172/1140), respectively, which had no significant difference (P = 0.056), but more susceptible to high-risk HPV infection after the age of 65 (P = 0.041). Except for 40 years old to menopause, the infection rate of high-risk HPV in this age group was different from that in postmenopause (P = 0.023, 0.729 (0.555, 0.957)), other age groups had no significant effect on high-risk HPV infection.ConclusionsIt was concluded that whether menopause has nothing to do with HPV infection. Moreover, the risk of high-risk HPV infection in women aged 40 to premenopausal is relatively low, but the infection rate increases after 65. Hence the cutoff screening age should be appropriately prolonged.

MXene-based ultra-thin film for terahertz radiation shielding

We have successfully fabricated Ti-based MXenes flakes, Ti3C2Tx, by chemical etching, then prepared it as an organic dispersion and finally spin-coated it on polyimide plastic substrate for terahertz wave shielding. The shielding effectivity of the 12 μm ultra-thin film can reach up to 17 dB measured by the terahertz time-domain spectra. We can attribute the excellent phenomenon to the intrinsic absorption of triple-layered Ti3C2, due to the similar double-peak type refraction curves, which have been respectively observed from the experimental samples and the simulation ones. High conductivity and strong THz absorption indicate the Ti3C2Tx MXene is the absorptive electromagnetic shielding material. Comparing with other kinds of THz shielding materials, the Ti-based MXenes might be a potential candidate for the next generation of ultra-thin and lightweight THz shielding.

Numerical analysis on the features of road deformation in the construction process of heat supply pipeline works

Shallow Tunneling Method has been widely applied in the construction of pipe gallery. However, due to the complexity of strata and the particularity of environment, improper construction may cause uneven settlement of urban road, even pavement collapse. In the paper, in reliance on Beijing Xi’anmen Street Heat Supply Pipeline Works and by virtue of drilling and survey, the engineering geological conditions and pavement structure of the target area were ascertained, Finite Element Method was utilized for numerical calculation, so as to determine the surface settlement & deformation laws under different construction situations, including the change law of longitudinal and lateral pavement settlement following the progress of excavation, and also the final pavement settlement and settlement scope, etc. It was found by research that, under the joint action of variable section of pipe gallery and shaft pipeline, the section height of pipe gallery has marked effect on the change of pavement settlement, the settlement speed of pavement monitoring point appears to be “double-peak type”.

Geochemical characteristics and exploration potential of Jurassic coal-formed gas in northwest China

Jurassic coal-measure strata are widely developed in Northwest China and mainly distributed in the Tarim Basin, Junggar Basin, Qaidam Basin, and Tuha Basin. The Jurassic coal-formed gas resources are abundant. Although the Jurassic strata in Northwest China have similar tectonic and sedimentary environments, the geochemical characteristics of the coal-formed gas formed in Northwest China have both similarities and differences. Therefore, analyzing and summarizing the geochemical characteristics and exploration potential of the coal-formed gas in the Jurassic petroleum systems in different basins are of great significance for searching for different types of coal-formed gases. Through comprehensive comparison and analysis, it is believed that the drying coefficient of Jurassic coal-formed gases in western China present three types: namely the single peak type of wet gas, the double peak type wet gas-dry gas and the single peak type dry gas; the distribution range of δ13C1 is large, corresponding to the sequence of source rocks from low maturity to over-mature; the partial isotopic inversion of C2 and C3 is mainly caused by the mixed source and biological actions; source rock maturity is the main reason causing the geochemical differences of natural gases in different regions. The Jurassic coal-formed gas in Northwest China has large exploration potential, and the exploration degree of structural gas reservoirs is relatively high. The structural-lithological and lithological gas reservoirs, as well as the main exploration reservoir types for Jurassic coal-formed gas in Northwest China; the Jurassic system in the Kuqa Depression of Tarim Basin, Cretaceous-Jurassic system in the southern margin of the Junggar Basin, the Jurassic high maturity coal-formed gas in the Tuha Basin and the Jurassic high maturity–post-mature coal-formed gas in the Qaidam Basin have great exploration potential, which are important exploration fields for Jurassic coal-formed gas in Northwest China in the future.

ZTF18aalrxas: A Type IIb Supernova from a Very Extended Low-mass Progenitor

Abstract We investigate ZTF18aalrxas, a double-peaked Type IIb core-collapse supernova (SN) discovered during science validation of the Zwicky Transient Facility. ZTF18aalrxas was discovered while the optical emission was still rising toward the initial cooling peak (0.7 mag over 2 days). Our observations consist of multi-band (ultraviolet and optical) light curves (LCs), and optical spectra spanning from ≈0.7 to ≈180 days past the explosion. We use a Monte-Carlo based non-local thermodynamic equilibrium model that simultaneously reproduces both the 56Ni-powered bolometric LC and our nebular spectrum. This model is used to constrain the synthesized radioactive nickel mass (0.17 M ☉) and the total ejecta mass (1.7 M ☉) of the SN. The cooling emission is modeled using semi-analytical extended envelope models to constrain the progenitor radius (790–1050 R ⊙) at the time of explosion. Our nebular spectrum shows signs of interaction with a dense circumstellar medium (CSM), and this spectrum is modeled and analyzed to constrain the amount of ejected oxygen (0.3–0.5 M ☉) and the total hydrogen mass (≈0.15 M ☉) in the envelope of the progenitor. The oxygen mass of ZTF18aalrxas is consistent with a low (12–13 M ☉) zero-age main-sequence mass progenitor. The LCs and spectra of ZTF18aalrxas are not consistent with massive single-star SN Type IIb progenitor models. The presence of an extended hydrogen envelope of low mass, the presence of a dense CSM, the derived ejecta mass, and the late-time oxygen emission can all be explained in a binary model scenario.

Multi-point micro-flame ignited hybrid lean-burn combustion of gasoline with direct injection dimethyl ether

Lean-burn combustion is effective in reducing fuel consumption of gasoline engines because of the higher specific heat ratio of the fuel lean mixture and reduced heat loss from lower combustion temperature. However, its application to real engines is hampered by the unstable ignition, high cyclic variability, and partial-burn due to slower combustion, as well as the restricted maximum lean-burn air/fuel ratio limit and the insufficiently low nitrogen oxides emission. Multi-point micro-flame-ignited hybrid combustion has been proposed and applied to extend the lean burn limit of premixed gasoline and air mixture. To achieve micro-flame-ignited combustion in premixed lean gasoline mixture formed by port fuel injection, a small amount of dimethyl ether is injected directly into the cylinder of a four-stroke gasoline engine to control and accelerate the ignition and combustion process so that the engine could be operated with the overall excess air coefficient (Lambda) of 1.9. The results show that heat release processes can be grouped into three forms, that is, ramp type, double-peak type, and trapezoid type. Regardless of single or split injections, direct injection timing of dimethyl ether dominates the features of heat release. The ramp type occurs at early injection timing while the double-peak type takes place at late injection timing. Trapezoid type appears between the above two types. Dimethyl ether injection timing controls the ignition timing and has less effect on combustion duration. Single injection of dimethyl ether leads to much earlier ignition timing and slightly longer combustion duration, forming higher nitrogen oxides emissions than the split injections. Ultra-low nitrogen oxides emissions and higher thermal efficiency are achieved in the ramp type combustion compared to the other two types of combustion in both injection approaches.

Finite Difference Method in Stress Analysis of Anchorage Zone of Highway Extradosed Cable Stayed Bridge

With the development and wide application of extradosed cable stayed bridge, an effective method is needed for simulation of the stress distribution in anchorage zone, which plays a vital role in transferring force from the cable to the pylon and diverting the cable direction. Based on the Finite Difference Method (FDM), an efficient and practical method of stress filed simulation was presented in the paper. First, a plane finite element model was established using ABAQUS, to determine the boundary condition for FDM. Based on this, FDM was used to simulate the stress distribution of the concrete in the anchorage zone. Finally, on the simulation result was calculated and in comparison with finite element model result. It has been found that: The vertical compressive stress of concrete in the anchorage zone gradually reduces from the middle to the two sides, and the stress assumes double peak type in transverse. Compared with the finite element solutions, the approximate solution simulated by FDM improve the computational efficiency with certain accuracy keeping, except the loading area. In vertical orientation, the concrete in the place of H (the width of the pylon) from cable force acting position is in a state of uniform stress.

Connecting the progenitors, pre-explosion variability and giant outbursts of luminous blue variables with Gaia16cfr

We present multi-epoch, multi-colour pre-outburst photometry and post-outburst light curves and spectra of the luminous blue variable (LBV) outburst Gaia16cfr discovered by the Gaia satellite on 1 December 2016. We detect Gaia16cfr in 13 epochs of Hubble Space Telescope imaging spanning phases of 10 yr to 8 months before the outburst and in Spitzer Space Telescope imaging 13 years before outburst. Pre-outburst optical photometry is consistent with an 18 Msun F8 I star, although the star was likely reddened and closer to 30 Msun. The pre-outburst source exhibited a significant near-infrared excess consistent with a 120 AU shell with 4x10-6 Msun of dust. We infer that the source was enshrouded by an optically-thick and compact shell of circumstellar material from an LBV wind, which formed a pseudo-photosphere consistent with S Dor-like variables in their "maximum" phase. Within a year of outburst, the source was highly variable on 10-30 day timescales. The outburst light curve closely matches that of the 2012 outburst of SN 2009ip, although the observed velocities are significantly slower than in that event. In Halpha, the outburst had an excess of blueshifted emission at late times centred around -1500 km/s, similar to that of double-peaked Type IIn supernovae and the LBV outburst SN 2015bh. From the pre-outburst and post-outburst photometry, we infer that the outburst ejecta are evolving into a dense, highly structured circumstellar environment from precursor outbursts within years of the December 2016 event.

Study on natural population dynamics and spatial distribution pattern of Tyrophagus putrescentiae in stored flour

To understand the natural population dynamics and spatial distribution of Tyrophagus putrescentiae in storage flour, so as to provide an evidence for its prevention and control. The samples from five sampling points in Wuhu City were collected monthly from January to December, 2013, and examined and counted for T. putrescentiae. The dispersion pattern target, Iwao's m*- x̄; regression analysis and Taylor's lgS2-lg x̄; regression analysis were used for analyzing the spatial distribution pattern of T. putrescentiae in the storage flour. The peaks of population dynamics of T. putrescentiae were discovered in July and September. The indexes of dispersion were as follows：I > 0, CA > 0, m*/ x̄; > 1; and the linear regression equation of Iwao：m* = 3.740 3 + 1.017 5 x̄; (r = 0.995 8) and Taylor：lgS2 = 0.500 4 + 1.134 9 lg x̄; (r =0.832 8) showed that the spatial distribution pattern of T. putrescentiae in the storage flour was assembled. The peak of population dynamics of T. putrescentiae in the storage flour in Wuhu City is a double peak type, and the spatial distribution pattern of T. putrescentiae is assembled.