结露工况下平行流蒸发器性能模拟研究

通过对百叶窗翅片平行流蒸发器空气侧换热性能进行数值模拟,分析了翅片间距、百叶窗间距和角度对空气侧流动特性、换热性能和结露过程的影响,得到了不同情况下空气侧进出口压降、换热系数及蒸发器表面凝结水量的变化规律。研究表明:百叶窗间距增加导致空气进出口压降增大,空气侧换热系数和蒸发器表面凝水量则随之呈现先增后减的趋势;翅片间距增加造成空气侧进出口压降、换热系数和蒸发器表面凝结水量逐渐减小;百叶窗角度增加使空气侧进出口压降、换热系数和蒸发器表面凝水量逐渐增大。综合考虑,当压降在可以接受的范围内时,可考虑选择较小的翅片间距、较大的百叶窗角度,百叶窗间距范围在1.4mm~1.6mm间为佳。     

Exponential stability for a one‐dimensional compressible viscous micropolar fluid

In this paper, we consider one‐dimensional compressible viscous and heat‐conducting micropolar fluid, being in a thermodynamical sense perfect and polytropic. The homogenous boundary conditions for velocity, microrotation, and temperature are introduced. This problem has a global solution with a priori estimates independent of time; with the help of this result, we first prove the exponential stability of solution in (H¹(0,1))⁴, and then we establish the global existence and exponential stability of solutions in (H²(0,1))⁴ under the suitable assumptions for initial data. The results in this paper improve those previously related results. Copyright © 2015 John Wiley & Sons, Ltd.     

An investigation of teachers’ intentions and reflections about using Standards-based and traditional textbooks in the classroom

This study analyzed teachers’ intentions for and reflections on their use of Standards-based [Connected Mathematics Program (CMP)] textbooks and traditional (non-CMP) mathematics textbooks to guide instruction. In this investigation of the interplay between textbooks and instruction, we focused on learning goals, instructional tasks, teachers’ anticipation of students’ difficulties, and their perceptions of students’ achievement of learning goals. All of these are aspects of teachers’ intentions and reflections that have proved fruitful in comparing the roles of the CMP and non-CMP mathematics textbooks in our Longitudinal Investigation of the Effect of Curriculum on Algebra Learning project. Whereas the cognitive level of the teachers’ intended learning goals appeared generally to reflect the emphases of their respective textbooks, we found that the CMP teachers’ intended learning goals were not as well aligned with the CMP textbooks as the non-CMP teachers’ learning goals were aligned with their non-CMP textbooks. The CMP and non-CMP teachers’ implementations of the lessons seemed to reduce the degree of difference between the cognitive levels of their intended goals. Even so, we found that significantly more CMP lessons than non-CMP lessons were implemented at a high level of cognitive demand. Although the non-CMP teachers’ intended learning goals were better aligned with their textbook’s learning goals, we found that the CMP teachers were more likely than the non-CMP teachers to follow the guidance of their textbooks in designing and selecting instructional tasks for a lesson. Future research should consider other aspects of teachers’ intentions and reflections that may shed a broader light on the role of textbooks and curriculum materials in teachers’ crafting of instructional experiences for their students.     

Crystallographic and magnetic structure of HAVAR under high-pressure using diamond anvil cell (DAC)

Annealed (H1) and cold-rolled (H2) HAVAR has been studied using high-pressure synchrotron X-ray diffraction. A structural phase transformation was discovered at ～13 GPa at ambient temperature, transforming from m ??3 m (S.G. 225) to P 63/m m c (S.G. 194) symmetry. The transition was not reversible on pressure release. The low-pressure cubic phase was found to be more compressible than the high-pressure hexagonal phase. Conventional Mössbauer and NFS shows that the HAVAR is not magnetic at room temperature and no splitting is observed. The SQUID indicates a huge difference in the temperature dependence of the magnetic susceptibility between the cold Rolled HAVAR compared to the annealed HAVAR.     

Evidence of Autler-Townes splitting in high-order nonlinear processes

We demonstrate Autler-Townes (AT) splitting of four-wave mixing in an electromagnetically induced transparency window, which results from the destructive interference between a three-photon process and a five-photon process. The primary and secondary AT splittings are achieved via induced atomic coherence in a four-level Y-type atomic system. Theoretical calculations fit well with the experimentally measured results. Such controlled multichannel splitting of nonlinear optical signals can have potential applications in optical communication and quantum information processing.     

Size dependent 2p3/2 binding-energy shift of Ni nanoclusters on SiO2 support: Skin-depth local strain and quantum trapping

An in situ X-ray photoelectron emission investigation revealed that the size trend of the 2p_3/2 binding-energy shift (BES) of Ni nanoclusters grown on SiO₂ substrate follows the prediction of the bond order-length-strength (BOLS) correlation theory [30]. Theoretical reproduction of the measurements turns out that the 2p_3/2 binding energy of an isolated Ni atom is 850.51 eV and its intrinsic bulk shift is 2.70 eV. Findings confirmed that the skin-depth local strain and potential well quantum trapping induced by the shorter and stronger bonds between under-coordinated surface atoms provide perturbation to the Hamiltonian and hence dominate the size dependent BES.     

Multivariate F-splines and Fractional Box Splines

We introduce multivariate F-splines, including multivariate F-truncated powers T _f (?|M) and F-box splines B _f (?|M). The classical multivariate polynomial splines and multivariate E-splines can be considered as a special case of multivariate F-splines. We document the main properties of T _f (?|M) and B _f (?|M). Using T _f (?|M), we extend fractional B-splines to fractional box splines and show that these functions satisfy most of the properties of the traditional box splines. Our work unifies and generalizes results due to Dahmen-Micchelli, de Boor-Höllig, Ron and Unser-Blu, and also presents a new tool for computing the integration over polytopes.     

ToF-SIMS investigation of octadecylphosphonic acid monolayers on a mica substrate

In this paper, time-of-flight secondary ion mass spectrometry (ToF-SIMS) under static conditions was used to investigate self-assembled monolayers (SAMs) of octadecylphosphonic acid (OPA) formed on freshly cleaved muscovite mica substrates. The coverage of OPA on mica ranged from 20 to 100%, with a film thickness of 1.7+/-0.2 nm, which was determined by atomic force microscopy (AFM) imaging. The relative intensity of the specific secondary ion species associated with the OPA and with the exposed mica substrate exhibited good correlation with surface coverage. An excellent correlation was also observed (R2=0.98) between the relative SIMS [OPA-H]- intensity and the surface carbon concentration (OPA C 1s, in atomic %) from XPS at the prescribed surface coverage. The observation of positive and negative OPA molecular attachment of secondary ions involving the substrate species is discussed in terms of the chemical affinity of the OPA phosphonate headgroup for the cleaved mica surface as well as the sampling depth. In addition, the OPA molecular attachment species formed with the potassium ions on the cleaved mica substrate dominated the positive secondary ion mass spectrum in the high-mass range. A temperature-dependent, ToF-SIMS study employing in situ heating of a 100% coverage OPA monolayer revealed that the molecules begin to diffuse above approximately 80 degrees C, resulting in a decrease in the relative secondary ion yield of the OPA-specific secondary ions. This observation is hypothesized to be due to a decrease in the effective coverage of the substrate by the OPA molecules, which in turn could be due to the formation of multilayers upon heating in an effort to minimize the energy of the system. The interesting behavior of the novel OPA dimer species as a function of temperature is also reported. It was observed that the relative intensity of OPA and the mica-specific secondary ion peak intensities to that of Si (mica substrate) provides an effective means to estimate the change in coverage at elevated temperatures.     

Determination of nicotine in mainstream smoke on the single puff level by liquid-phase microextraction coupled to matrix-assisted laser desorption/ionization Fourier transform mass spectrometry

A method coupling liquid-phase microextraction with matrix-assisted laser desorption/ionization Fourier transform mass spectrometry (LPME/MALDI-FTMS) was developed to measure the content of nicotine in mainstream smoke at the single puff level. Glycerol was utilized as a matrix additive in the sample preparation to improve the homogeneity of analyte distribution in a sample spot. Good repeatability of the MALDI-MS signal (RSD <9%) was achieved by the method. Selective LPME facilitated the separation and purification of basic components from cigarette smoke. The LPME device was coupled to a smoking machine, and each puff of one cigarette could be gathered by this modified machine. The amount of nicotine in the mainstream smoke was measured at the single puff level by LPME/MALDI-FTMS. The method was simple and selective and was sufficiently sensitive to detect nicotine in each puff of one cigarette. The method thus offered an alternative approach to the study of the formation mechanism of cigarette smoke constituents.