Secondary electron emission from oxide-coated cathodes

The secondary electron emission from alkaline-earth oxide-coated cathodes has been investigated under both continuous and pulsed bombardment. Various factors affecting the yield, such as dependence upon primary voltage, collecting voltage, temperature, time, and angle of incidence, are noted, and the present state of the theory is discussed.Experiments have been performed with three types of apparatus. Yield vs. Energy data reveal values of δ of 4–7 at room temperature, with a more or less flat maximum at approximately 1,000 volts primary energy.The yield increases with temperature in an exponential manner, and plots of log Δδ (i.e. δ_K° ? δ_300°K) vs. 1/T give straight lines. Values of Q₁ between 0.9 – 1.5 eV. are generally indicated, and from extrapolation of these curves, yields exceeding 100 at 850° C. are deduced. The secondary emission depends upon the degree of activation, and increases with enhancement of the thermionic emission characteristics. Short-time effects such as growth or decay of secondary current after the onset of primary bombardment or persistence after the cessation of bombardment have not been observed, and values of yield obtained by pulsed methods are in accord with those obtained under D.C. conditions. Tail phenomena reported by J. B. Johnson and interpreted as “enhanced thermionic emission” from oxidecoated cathodes become manifest only under experimental conditions characterized by certain space-charge effects, and have been effectively simulated by bombarding a tantalum target adjacent to an electron-emitting tungsten filament. Various measurements of the energy distribution of secondary electrons as a function of primary voltage and temperature have been obtained. It was observed that the average energy of the secondary electrons decreases with temperature at a rate which more than compensates for the increase in the number of secondaries emitted per incident primary. The mechanism of the observed dependence of yield upon temperature is not well understood. Various alternative explanations are discussed and, in the light of the present state of our knowledge, regarded as untenable.     

A new three-dimensional heat flux-temperature integral relationship for half-space transient diffusion

This paper derives a new integral relationship between heat flux and temperature in a transient, three-dimensional heat conducting Cartesian half space (x>0, y∈(−∞,∞), z∈(−∞,∞)). A unified mathematical treatment has been developed based on operational and transform methods; and singular integral equation regularization. Regularization is accomplished based on a series of observations involving the diffusive nature of the operator. This newly developed relationship provides the local heat flux perpendicular to the front surface at any location within the half space. This expression suggests that an embedded plane of temperature sensors parallel to the surface can be used to acquire the local, in-depth heat flux in the x-direction. The relationship does not require a priori knowledge of the surface boundary condition which has analytically been removed in the process. The ill-posed nature of diffusion is highlighted owing to the appearance of the heating/cooling rate (°C/s) in the integrand of the new relationship. Integral relationships of this type are highly useful for experimental investigations since the in-depth heat flux can be extracted from well-established temperature transducers.     

Recurrent mirages at Puerto Peñasco,Sonora

Mirage behavior at Puerto Peñasco, on the Sonoran shore of the Gulf of California, is not only systematic, but is fully compatible with conditions of atmospheric refraction common in that arid area adjacent to a tropical sea. Images of mountains in Baja California, normally hidden below the visual horizon, are regularly loomed into visibility as the lapse rate in the lower layers of the atmosphere increases; and sink again below the horizon with the onset of nocturnal inversions. False sea horizons, due to refraction, are a standard midday condition; as are inferior mirages over adjacent land areas.Air stratification is normally accompanied by “paper doll” duplications of distant images; Fata Morgana is a common occurrence when cold air drainages from high mountains reach the warm waters of the Gulf of California. Photographic differentiation between mirage lakes and actual bodies of water is sometimes possible by use of deep red filters.     

An atmospheric dust recorder

An apparatus is described for recording general atmospheric dust. The full-scale range of the present model of approximately 120 × 10⁶ particles per cubic foot of air may be increased or decreased as desired. The dust concentrations measured are far below smoke concentrations. The method is to impinge dust on a slowly moving strip of transparent film, and to measure the deposit by a comparison of two beams of light, one passing through the dusty film, the other through clean film. The decrease in transmitted light due to the dust is balanced automatically by a motor-driven optical wedge in the unobstructed beam. The position of this wedge is recorded on a chart. Dusty air is sampled continuously for long periods. Rapid fluctuations of a few minutes in length are registered. In this, and in the fact that it is direct-reading, without tedious laboratory quantitation, the recorder offers distinct advantages over the present dust determinators, almost all of which take momentary samples. A different calibration is needed for different dusts. The machine may be adapted to laboratory or field use. In factories, auxiliary blowers may be operated through relays, when the dustiness exceeds a specified level.     

Temperature distribution in toroidal electrical coils of rectangular cross section

The essential content of a recent paper by the present writer comprises a comprehensive discussion of the physical bases underlying derivation of formulas for calculating the temperature distribution T, maximum temperature T_m and average temperature T_a in a toroidal electrical coil of rectangular cross section, internally generated heat and change of wire resistance with temperature being taken into account. Illustratively, the solution for the boundary value condition of constant surface temperature and uniform equivalent thermal conductivity was obtained.For the most part, however, problems that arise in practice are not encompassed in the comparatively simple boundary conditions of constant temperature. Experiment shows that in general the boundary condition is $\text{T ? T′ = ?}\text{K?}\text{?n}$; whereof n denotes the outward drawn normal to the coil surface, $\text{K = (}\text{k}{}_{\mathrm{n}}\text{h}\text{)}$ the ratio of the equivalent thermal conductivity in the direction of n to the emissivity of the boundary surface, and T and T′ are the corresponding temperatures in the coil surface and the immediately adjacent ambient medium. Again, it frequently ensues in practice that the thermal conductivity is substantially different in the directions of the two principal axes of the cross section.In the present paper formulas for T, T_m, and T_a are obtained for electrical coils of ratio of external to internal radius greater than (roughly) two whereof (i) the thermal conductivity is different in the directions of the two principal axes of the cross section, (ii) K is different on but constant over each of the four faces of the coil, and (iii) no restriction is made as to T′ except that over each face it be expressible in a generalized Fourier series. Determination of T is posed as a boundary-value problem in the mathematical theory of heat; the formal solution of T effected by expansions in orthogonal functions; and T_m and T_a then determined through use of their known relationships with T. The resulting formulas are in the form of rapidly-converging singly-infinite trigonometric-hyperbolic series. Illustrative of application of these general formulas, the maximum temperatures in a coil of given dimensions subject to two different sets of surface conditions are calculated and found to be in excellent agreement with the known measured values.The just-mentioned formulas encompass practically all cases encountered in practice except those coils which do not satisfy the restriction as to ratio of radii. For these latter formulas for T, T_m, and T_a are obtained pursuant to conditions of (i) equivalent thermal conductivity different in the directions of the two principal axes of the cross section, (ii) K, and likewise T′, different on but constant over each of the four faces of the coil. These formulas are in the form of rapidly-converging singly-infinite trigonometric- Bessel function (of zero order) series: Illustratively, the maximum temperature in a coil of given dimensions is calculated and found to be in excellent agreement with the known measured value.     

Combined strategies for improving production of a thermo-alkali stable laccase in Pichia pastoris

BackgroundLaccases are copper-containing enzymes which have been used as green biocatalysts for many industrial processes. Although bacterial laccases have high stabilities which facilitate their application under harsh conditions, their activities and production yields are usually very low. In this work, we attempt to use a combinatorial strategy, including site-directed mutagenesis, codon and cultivation optimization, for improving the productivity of a thermo-alkali stable bacterial laccase in Pichia pastoris.ResultsA D500G mutant of Bacillus licheniformis LS04 laccase, which was constructed by site-directed mutagenesis, demonstrated 2.1-fold higher activity when expressed in P. pastoris. The D500G variant retained similar catalytic characteristics to the wild-type laccase, and could efficiently decolorize synthetic dyes at alkaline conditions. Various cultivation factors such as medium components, pH and temperature were investigated for their effects on laccase expression. After cultivation optimization, a laccase activity of 347 ± 7 U/L was finally achieved for D500G after 3 d of induction, which was about 9.3 times higher than that of wild-type enzyme. The protein yield under the optimized conditions was about 59 mg/L for D500G.ConclusionsThe productivity of the thermo-alkali stable laccase from B. licheniformis expressed in P. pastoris was significantly improved through the combination of site-directed mutagenesis and optimization of the cultivation process. The mutant enzyme retains good stability under high temperature and alkaline conditions, and is a good candidate for industrial application in dye decolorization.     

The variation of the residual ionization with pressure at different altitudes,and its relation to the cosmic radiation

Measurements have been made of the residual ionization in a closed vessel of steel one inch thick, shielded by a two inch casing of lead, over a range of pressure from atmospheric to one thousand pounds per sq. inch, at Pike's Peak (alt. 14,000 ft.), Colorado Springs (alt. 6,ooo ft.), and New Haven (alt. 6,000 ft.). The ionization-pressure curves presents features of interest in relation to the interpretation of the processes associated with ionization in the vessel. However, in the present investigation they are used simply to obtain average relative value of the ionization due to the cosmic rays at the three altitudes concerned. A method of correcting the observations for absorption by the iron sphere, the lead case, and the walls of the buildings, has been developed. It is found that the data for the three stations can be correlated by the assumption of a pair of frequencies in the original cosmic radiation; and, as a matter of fact, an infinite number of such pairs are possible. They are represented in graphical form in Fig. 7 If we permit the assumption of three different frequencies in the cosmic radiation, it is possible in general to assign two of the frequencies, and determine an infinite number of possibilities as regards the third, distributed over a definite range. The possibilities inherent in the assumption of three frequencies are contained in tabular form in Table XVII. Of course, the inclusion of observations from more than three altitudes would serve to fix more definitely the possibility as regards the analysis. However, the result of the analysis for the three stations concerned is possibly of interest for comparison with other data, and as an indication of the kind of information which it is possible to extract from observations of this kind. It is probable that the very large range of possibilities inherent in a solution with three coefficients of absorption will be rather surprising to anyone who considers a situation of this kind for the first time.In addition to those whose assistance has already been acknowledged, I wish to acknowledge the assistance of Professor J. W. Broxon, who visited me while on Pike's Peak, and assisted in setting up the apparatus; and my thanks are due to Mr. C. A. Kotterman, and particularly to Mr. Andrew Longacre, and Mr. W. E. Ramsey for assistance in the reduction of the observations, and in the computational work.     

2013年后中国大气雾霾治理对经济发展的影响分析——以京津冀地区为案例

在大气雾霾治理进程中,认为大气雾霾治理对中国经济发展带来负面影响是当前的一个主导想法,这导致政府对进一步改善大气质量产生为难情绪。文章采用2013—2018年的统计数据和实地调研数据,分析了潜在受影响部门的产量、盈利及新兴产业的发展。并以环保产业作为案例,说明大气雾霾治理对经济发展的作用。研究结果发现：和目前普遍认为的“大气雾霾治理对经济产生负面影响”的结论不一致,近年来大气雾霾治理的重点地区,特别是京津冀地区,在环境质量提升的同时,潜在受负面影响的行业经济也发展良好;此外,先行治理地区的相关环保产业发展良好,并引领全国。该结论对当前进一步深度大气治理仍存疑虑的地区有一定启发。地方政府可以充分利用大气雾霾治理的机会,将环境治理、大气雾霾治理,以及温室气体减排和本地产业发展结合起来,形成良性发展格局,促进本地经济发展。中国也应坚定不移地实现自身的环境根本性变革和CO₂深度减排,这既是人类命运共同体在环境、气候变化领域的体现,也是为中国企业在全球的发展提供的巨大机遇。     

北京市冬季大气颗粒物污染水平和影响因素研究

北京市大气颗粒物造成的城市空气污染仍是目前亟待解决的问题之一。为了分析北京市大气颗粒物的污染水平及其影响因素，作者以大气中的PM10 和PM2.5为研究对象，于2005年冬季在北京市范围内设立了5个功能区（9个采样点）进行采样监测。结果表明，北京市PM10 和PM2.5污染比较严重，不同区域的PM10 和PM2.5的污染程度为：交通干道区＞工业区，郊区＞商业区＞居民区，且PM2.5质量浓度的空间分布并不完全同于PM10；气象条件稳定时，PM10 和PM2.5质量浓度的日变化表现出一定的规律性，这种时间变化的特征主要取决于所在环境中排放的污染物变化情况；PM10 和PM2.5的污染程度受气象条件的影响：在一定的范围内，颗粒物质量浓度随着温度的上升而下降，随着相对湿度的升高而增加，随着风力的增强而降低，随逆温层的生成及增强而增高。     

Special functions of circuits and systems

The polynomial solutions of the equation fy″ + gy′ + λy = 0 are obtained and classified for f, g, and λ certain second-degree, first-degree, and zero-degree polynomials, respectively. Applications are given illustrating the use of these polynomials in the construction of amplitude functions and system functions and in tree counting. In particular, all-pole and rational filter functions are considered which include as special cases the Chebyshev, Butterworth, elliptic, Bessel, and various transitional filter functions.     

中国阿魏属的黄酮体成分及其分类学意义

通过对国产阿魏属(Ferula)16个种的化学分析，发现其中13个种含黄酮体成分， 包括槲皮素、山奈酚和芹菜素的糖甙，以槲皮素成分最普遍。这些成分多为伞形科植物所常 见，与对山芹属的研究结果较接近。未发现黄酮体的三个种，即新疆阿魏、阜康阿魏和托里阿 魏，均为具有强烈臭味的药用植物。本属近前胡亚属的国产种类常为分布于半湿润山坡的高 大草本，所含黄酮体以槲皮素糖甙为主，而分布于干旱生境的种所含化合物较复杂，除槲皮素外，还含有芹菜素和山奈酚成分。本文还根据黄酮体成分对部分种的系统位置作了讨论。     

Fault-tolerant computation in groups and semigroups: applications to automata,dynamic systems and Petri nets

The traditional approach to fault-tolerant computation has been via modular hardware redundancy. Although universal and simple, modular redundancy is inherently expensive and inefficient. By exploiting particular structural features of a computational architecture or an algorithm, arithmetic codes and recently developed algorithm-based fault tolerance (ABFT) techniques manage to introduce “analytical redundancy” and offer more efficient fault coverage at the cost of narrower applicability and harder design. In this paper, we extend a variety of results and constructive procedures that were developed in previous work for computations that take place in an abelian group to a more general setting that considers computations in semigroups. We demonstrate possible encodings for semigroup operations of interest and use our extension to design concurrent error detection and correction schemes for group and semigroup machines. The method provides insight regarding the role of decomposition in fault-tolerant algebraic machines and results in a general, hardware-independent characterization of concurrent error detection and correction in finite semiautomata. We also demonstrate that by extending this approach to other dynamic systems, with specific hardware implementations and failure modes, we can systematically obtain fault-tolerant architectures. More specifically, we apply these techniques to linear time-invariant dynamic systems and Petri net models of discrete event systems.     

Mannheimia haemolytica growth and leukotoxin production for vaccine manufacturing — A bioprocess review

Mannheimia haemolytica leukotoxin (LKT) is a known cause of bovine respiratory disease (BRD) which results in severe economic losses in the cattle industry (up to USD 1 billion per year in the USA). Vaccines based on LKT offer the most promising measure to contain BRD outbreaks and are already commercially available. However, insufficient LKT yields, predominantly reflecting a lack of knowledge about the LKT expression process, remain a significant engineering problem and further bioprocess optimization is required to increase process efficiency. Most previous investigations have focused on LKT activity and cell growth, but neither of these parameters defines reliable criteria for the improvement of LKT yields. In this article, we review the most important process conditions and operational parameters (temperature, pH, substrate concentration, dissolved oxygen level, medium composition and the presence of metabolites) from a bioprocess engineering perspective, in order to maximize LKT yields.     

Exploring atmospheric free-radical chemistry in China: the self-cleansing capacity and the formation of secondary air pollution

Since 1971, it has been known that the atmospheric free radicals play a pivotal role in maintaining the oxidizing power of the troposphere. The existence of the oxidizing power is an important feature of the troposphere to remove primary air pollutants emitted from human beings as well as those from the biosphere. Nevertheless, serious secondary air-pollution incidents can take place due to fast oxidation of the primary pollutants. Elucidating the atmospheric free-radical chemistry is a demanding task in the field of atmospheric chemistry worldwide, which includes two kinds of work: first, the setup of reliable radical detection systems; second, integrated field studies that enable closure studies on the sources and sinks of targeted radicals such as OH and NO₃. In this review, we try to review the Chinese efforts to explore the atmospheric free-radical chemistry in such chemical complex environments and the possible link of this fast gas-phase oxidation with the fast formation of secondary air pollution in the city-cluster areas in China.     

AVHRR全球时间序列研究进展：PAL-GIMMS-LTDR

AVHRR是1981年～2000年间主要的全球对地观测数据集,也是正在开发的跨传感器（AVHRR-MODIS-VIIRS）长期数据集的重要组成部分。由于AVHRR数据来自多个NOAA卫星,最初是为气象预报设计的,因此在利用AVHRR进行陆地生态系统研究时,虽然取得了最初设计AVHRR时所没有预料到的成绩,但是也不断遇到一些问题。对这些问题的不同处理,就形成了很多AVHRR数据集。本文从数据完整性、时空分辨率、地图投影、文件格式、传感器标定、卫星漂移校正、云检测、大气校正、数据构成与质量标记等方面,比较了3个主要的AVHRR数据集（PAL,GIMMS,LTDR）的特征。这些特征对重新评估基于各种AVHRR数据集研究报告的可靠性,合理使用不同AVHRR数据进行陆地生态系统长期变化研究,具有一定的参考意义。     

Being my own gatekeeper,how I tell the fake and the real – Fake news perception between typologies and sources

The phenomenal spread of fake news online necessitates further research into fake news perception. We stress human factors in misinformation management. This study extends prior research on fake news and media consumption to examine how people perceive fake news. The objective is to understand how news categories and sources influence individuals' perceptions of fake news. Participants (N = 1008) were randomly allocated to six groups in which they evaluated the believability of news from three categories (misinformation, conspiracy, and correction news) coupled with six online news sources whose background (official media, commercial media, and social media) and expertise level varied (the presence or absence of a professional editorial team). Our findings indicated people could distinguish media sources, which have a significant effect on fake news perception. People believed most in conspiracy news and then misinformation included in correction news, demonstrating the backfire of correction news. The significant interaction effects indicate people are more sensitive to misinformation news and show more skepticism toward misinformation on social media. The findings support news literacy that users are capable to leverage credible sources in navigating online news. Meanwhile, challenges of processing correction news require design measures to promote truth-telling news.     

Mathematical study of h-index sequences

This paper studies mathematical properties of h-index sequences as developed by Liang [Liang, L. (2006). h-Index sequence and h-index matrix: Constructions and applications. Scientometrics,69(1), 153–159]. For practical reasons, Liming studies such sequences where the time goes backwards while it is more logical to use the time going forward (real career periods). Both type of h-index sequences are studied here and their interrelations are revealed. We show cases where these sequences are convex, linear and concave. We also show that, when one of the sequences is convex then the other one is concave, showing that the reverse-time sequence, in general, cannot be used to derive similar properties of the (difficult to obtain) forward time sequence. We show that both sequences are the same if and only if the author produces the same number of papers per year. If the author produces an increasing number of papers per year, then Liang’s h-sequences are above the “normal” ones. All these results are also valid for g- and R-sequences. The results are confirmed by the h-, g- and R-sequences (forward and reverse time) of the author.     

An extension of the general Struble's method for solving an nth order nonlinear differential equation when the corresponding unperturbed equation has some repeated eigenvalues

This paper attempts to show the more suitability of the extended general Struble's technique than the unified Krylov-Bogoliubov-Mitropolskii (KBM) method in solving the problems that occur during the critical conditions. Recently a critically damped condition of an nth, n=2,3, … order weakly nonlinear autonomous ordinary differential equation has been investigated by the unified KBM method, in which the corresponding unperturbed equation has some real (negative) repeated eigenvalues. But there are more important critical conditions, which are still untouched. One of them occurs when a pair of complex eigenvalues is equal to another. It is complicated to formulate as well as to utilize the KBM method to investigate this condition. However, the extended general Struble's technique is applicable to both autonomous and non-autonomous systems. Solutions obtained for different critical conditions as well as for different initial conditions show a good agreement with the numerical solutions. The method is illustrated by an example of a fourth-order nonlinear differential equation whose unperturbed equation has repeated complex eigenvalues. A steady-state solution is determined for the non-autonomous equation. Moreover, a critical condition of a fourth-order nonlinear equation is investigated when two real eigenvalues of the unperturbed equation are non-positive and equal.     

Studying the effect and treatment of misspelled queries in Cross-Language Information Retrieval

In contrast with their monolingual counterparts, little attention has been paid to the effects that misspelled queries have on the performance of Cross-Language Information Retrieval (CLIR) systems. The present work makes a first attempt to fill this gap by extending our previous work on monolingual retrieval in order to study the impact that the progressive addition of misspellings to input queries has, this time, on the output of CLIR systems. Two approaches for dealing with this problem are analyzed in this paper. Firstly, the use of automatic spelling correction techniques for which, in turn, we consider two algorithms: the first one for the correction of isolated words and the second one for a correction based on the linguistic context of the misspelled word. The second approach to be studied is the use of character n-grams both as index terms and translation units, seeking to take advantage of their inherent robustness and language-independence. All these approaches have been tested on a from-Spanish-to-English CLIR system, that is, Spanish queries on English documents. Real, user-generated spelling errors have been used under a methodology that allows us to study the effectiveness of the different approaches to be tested and their behavior when confronted with different error rates. The results obtained show the great sensitiveness of classic word-based approaches to misspelled queries, although spelling correction techniques can mitigate such negative effects. On the other hand, the use of character n-grams provides great robustness against misspellings.