分类: 核科学技术 >> 核材料与工艺技术 提交时间: 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要: Polyvinyl alcohol (PVA) is a well-known friendly polymer for paper-making, textiles, and a variety of coatings, biomedical applications such as artificial pancreas, synthetic vitreous body, wound dressing, artificial skin, and cardiovascular device. In this paper, ion/electron beam is employed to get insight into the irradiation effect on surface morphology and optical properties of PVA polymer. UV-Vis spectra are recorded to investigate the effect of induced defects on the optical band gap and the formed carbon clusters size. Scanning electron microscopy (SEM) is used to relate and investigate surface morphology and optical properties of the target polymer with different doses (15, 30 and 60 min). Also, PVA polymer is subjected to theoretical studies by using semi-empirical PM7 quantum chemical method.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We investigate the properties of the mixed-mode (RRd) RR Lyrae (RRL) variables in the Fornax dwarf spheroidal (dSph) galaxy by using $B$- and $V$-band time series collected over twenty-four years. We compare the properties of the RRds in Fornax with those in the Magellanic Clouds and in nearby dSphs, with special focus on Sculptor. We found that the ratio of RRds over the total number of RRLs decreases with metallicity. Typically, dSphs have very few RRds with 0.49$\ltsim P_0 \ltsim $0.53 days, but Fornax fills this period gap in the Petersen diagram (ratio between first overtone over fundamental period versus fundamental period). We also found that the distribution in the Petersen diagram of Fornax RRds is similar to SMC RRds, thus suggesting that their old stars have a similar metallicity distribution. We introduce the Period-Amplitude RatioS (PARS) diagram, a new pulsation diagnostics independent of distance and reddening. We found that LMC RRds in this plane are distributed along a short- and a long-period sequence that we identified as the metal-rich and the metal-poor component. These two groups are also clearly separated in the Petersen and Bailey (luminosity amplitude versus logarithmic period) diagrams. These circumstantial evidence indicates that the two groups have different evolutionary properties. All the pulsation diagnostics adopted in this investigation suggest that old stellar populations in Fornax and Sculptor dSphs underwent different chemical enrichment histories. Fornax RRds are similar to SMC RRds, while Sculptor RRds are more similar to the metal-rich component of the LMC RRds.
分类: 物理学 >> 核物理学 提交时间: 2016-09-06
摘要: We study microscopic processes responsible for chirality flips in the thermal bath of Quantum Chromodynamics at finite temperature and zero baryon chemical potential. We focus on the temperature range where the crossover from chirally broken phase to quark-gluon plasma takes place, namely T≃(150,200) MeV. The processes we consider are quark-quark scatterings mediated by collective excitations with the quantum number of pions and σ-meson, hence we refer to these processes simply as \sugg{to} one-pion (one-σ) exchange\sugg{s}. We use a Nambu-Jona-Lasinio model to compute equilibrium properties of the thermal bath, as well as the relevant scattering kernel to be used in the collision integral to estimate the chiral relaxation time τ. We find τ≃0.1÷1 fm/c around the chiral crossover.
分类: 物理学 >> 核物理学 提交时间: 2016-09-12
摘要: We search for a light Higgs boson A0 in the fully reconstructed decay chain of J/ψ→γA0, A0→μ+μ− using(225.0±2.8)×106 J/ψ events collected by the BESIII experiment. The A0 is a hypothetical CP-odd light Higgs boson predicted by many extensions of the Standard Model including two spin-0 doublets plus an extra singlet. We find no evidence for A0 production and set 90% confidence-level upper limits on the product branching fraction B(J/ψ→γA0)×B(A0→μ+μ−) in the range of (2.8−495.3)×10−8 for 0.212≤mA0≤3.0GeV/c2. The new limits are 5 times below our previous results, and the nature of the A0 is constrained to be mostly singlet.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: The statistical properties of wave chaotic systems of varying dimensionalities and realizations have been studied extensively. These systems are commonly characterized by the statistics of the eigenmode-spacings and the statistics of the eigenfunctions. Here, we propose photonic crystal (PC) defect waveguide graphs as a new physical setting for chaotic graph studies. Photonic crystal waveguides possess a dispersion relation for the propagating modes which is engineerable. Graphs constructed by joining these waveguides possess junctions and bends with distinct scattering properties. We present numerically determined statistical properties of an ensemble of such PC-graphs including both eigenfunction amplitude and eigenmode-spacing studies. Our proposed system is compatible with silicon nanophotonic technology and opens chaotic graph studies to a new community of researchers.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-11-02 合作期刊: 《热科学学报》
摘要: The pintle injector used for a liquid rocket engine is a newly re-attracted injection system famous for its wide throttle ability with high efficiency. The pintle injector has many variations with complex inner structures due to its moving parts. In order to study the rotating flow near the injector tip, which was observed from the cold flow experiment using water and air, a numerical simulation was adopted and a verification of the numerical model was later conducted. For the verification process, three types of experimental data including velocity distributions of gas flows, spray angles and liquid distribution were all compared using simulated results. The numerical simulation was performed using a commercial simulation program with the Eulerian multiphase model and axisymmetric two dimensional grids. The maximum and minimum velocities of gas were within the acceptable range of agreement, however, the spray angles experienced up to 25% error when the momentum ratios were increased. The spray density distributions were quantitatively measured and had good agreement. As a result of this study, it was concluded that the simulation method was properly constructed to study specific flow characteristics of the pintle injector despite having the limitations of two dimensional and coarse grids.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2016-07-19
摘要: We explore the possibility that the observed baryon asymmetry of the Universe is the result of an earlier phase transition in which an extended gauge sector breaks down into the SU(3)(C)xSU(2)(L)xU(1)(Y) of the standard model. Our proto-typical example is the topflavor model, in which there is a separate SU(2)(1) for the third generation from the SU(2)(2) felt by the first two generations. We show that the breakdown of SU(2)(1)xSU(2)(2)-> SU(2)(L) results in lepton number being asymmetrically distributed throughout the three families, and provided the SM electroweak phase transition is not strongly first order, results in a nonzero baryon number, which for parameter choices that can be explored at the LHC may explain the observed baryon asymmetry.
分类: 地球科学 >> 地球科学史 提交时间: 2020-10-20 合作期刊: 《干旱区科学》
摘要: Savanna woodlands in Sudan host great biodiversity, provide a plethora of ecosystem goods and services to local communities, and sustain numerous ecological functions. Although the importance of the Acacia trees in these areas is well known, up-to-date information about these woodlands' diversity is limited and changes in their woody vegetation composition, density, diversity and relative frequency are not monitored over time. This study explored tree diversity and stand stage structure in Nuara Reserved Forest, a typical savanna woodland ecosystem in southeastern Sudan. A total of 638 circular sample plots (1000 m2 for each) were established using a systematic sampling grid method. The distance between plots was 200 m. In each plot, all living trees with diameter at breast height (DBH) ≥5.00 cm were identified and counted, and their DBH values were recorded. From these data, tree composition, diversity, density and stage structure were assessed. There were 12,259 individual trees representing four species (Acacia seyal, Balanites aegyptiaca, Acacia Senegal and Acacia mellifera) that belong to two families. The dominant species was Acacia seyal. Average tree density was 191 trees/hm2 and the Shannon-Weiner index for trees diversity was 0.204. Overall, young trees comprised 86.30% of the forest. The state of tree richness and density in the study area was low compared to other similar environments in the region and around the world. We recommended adoption of a proper management system that includes monitoring of woody vegetation diversity in this forest, and management actions to enhance tree diversity and sustain ecosystem services to local communities. In addition to care for the dominant Acacia seyal stands, more attention and conservation should be devoted to reestablishing Acacia senegal and Acacia mellifera trees because of their high ecological and economic values for local communities.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: A well-established, comprehensive 3-D numerical modulation model is applied to simulate galactic protons, electrons and positrons from May 2011 to May 2015, including the solar magnetic polarity reversal of Solar Cycle 24. The objective is to evaluate how these simulations compare with corresponding AMS observations for 1.0-3.0 GV, and what underlying physics follows from this comparison in order to improve our understanding on how the major physical modulation processes change, especially particle drift, from a negative to a positive magnetic polarity cycle. Apart from their local interstellar spectra, electrons and positrons differ only in their drift patterns, but they differ with protons in other ways such as their adiabatic energy changes at lower rigidity. In order to complete the simulations for oppositely charged particles, antiproton modeling results are obtained as well. Together, the observations and the corresponding modeling indicate the difference in the drift pattern before and after the recent polarity reversal and clarify to a large extent the phenomenon of charge-sign dependence during this period. The effect of global particle drift became negligible during this period of no well-defined magnetic polarity. The resulting low values of all particles' MFPs during the polarity reversal contrast their large values during solar minimum activity, and as such expose the relative contributions and effects of the different modulation processes from solar minimum to maximum activity. We find that the drift scale starts recovering just after the polarity reversal, but the MFPs keep decreasing or remain unchanged for some period after the polarity reversal.
分类: 地球科学 >> 水文学 提交时间: 2022-03-15 合作期刊: 《干旱区科学》
摘要: It is common knowledge that Yarmouk River Basin (YRB) is shared between Jordan and Syria. Management of YRB trans-boundary water resources is attracting increasing interest because it is a strategic water resource for the riparian countries. Actually, lack of sharing information regarding hydrological flows and basin's water management between partners' countries makes it difficult to distinguish between natural and man-made factors affecting the water body. Therefore, this study seeks to address and assess the main on-site changes that exert on YRB. Geospatial technique and arithmetic equations were combined to carry out an assessment of the changes on water resources in YRB. Data, information and field measurements of the basin were aggregated, compiled and presented to determine the extent of changes during the period 19802020. Remarkable findings showed that precipitation amount in the basin significantly declined during the period 19802020 in particularly after the year 1992. Pumping rate of groundwater was 550103 m3/a, exceeding the basin's safe yield. Draw down of static groundwater level over time approached the value of 3.2 m/a due to the over abstraction in the aquifer body. Additionally, the evaporation rate reached more than 99% in some regions in the basin. Moreover, the number of private wells has increased from 98 wells in 1980 to 126 wells in 2020, showing the excessive extraction of groundwater. These findings indicate that the study area is subjected to a considerable groundwater depletion in the near future due to extensive abstraction, continuous drilling of illegal wells and decreased annual precipitation under the shadow of the rapid population growth and continuous influx of refugees. Therefore, decision makers-informed scenarios are suggested in the development of water resource portfolios, which involves the combination of management and infrastructural actions that enhance the water productivity of the basin. Further studies are recommended to evaluate the on-site changes on water resources in YRB in collaboration with riparian countries and to establish monitoring system for continuous and accurate measurements of the basin.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-11-10
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-11-10
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-11-10
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-11-10
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-11-10
摘要: Using an electron-positron collision data sample of 2.93 fb collected at a center-of-mass energy of √s = 3.773 GeV with the BESIII detector, we present the first search for the radiative leptonic decay D+ →+γe+νe.+ The analysis is performed with a double tag method. We do not+ observ+e a significant D → γe νe signal, and obtain an upper limit on the branching fraction of D → γe νe decay with the energy of radiative photon larger than 10 MeV of 3.0 × 10 at the 90% confidence level.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-11-10
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-11-10
摘要: By analyzing the large-angle Bhabha scattering events e+e− → (γ)e+e and diphoton events e e → γγ for the data sets collected at center-of-mass (c.m.) energies between 2.2324 and 4.5900 GeV (131 energy points in total) with the upgraded Beijing Spectrometer (BESIII) at the Beijing Electron-Positron Collider (BEPCII), the integrated luminosities have been measured at the different c.m. energies, individually. The results are the important inputs for R value and J/ψ resonance parameter measurements.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-11-10
摘要: We present an amplitude analysis of the decay D0 → K−π+π+π− based on a data sample of 2.93 fb−1 acquired by the BESIII detector at the ψ(3770) resonance. With a nearly background free sample of about 16000 events, we investigate the substructure of the decay and determine the relative fractions and the phases among the different intermediate processes. Our amplitude model includes the two-body decays D0 → K¯ ∗0ρ0, D0 → K−a+(1260) and D0 → K−(1270)π+, the three-body decays D0 → K¯ ∗0π+π− and D0 → K−π+ρ0, as well as the four-body nonresonant decay D0 → K−π+π+π−. The dominant intermediate process is D0 → K−a+(1260), accounting for a fit fraction of 54.6%.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-11-10
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-11-10