Criteria for Selection of a Subset Regression: Which One Should Be Used?

The problem of selecting the best subset of predictor variables in a linear regression model has led to the development of a number of criteria for choosing between contending subsets. Unfortunately, the properties of these criteria are generally not understood and the relative merits of contending criteria are not clear. In this note, a number of criteria are reviewed and a cooperative effort to resolve the problem is recommended.     

Effect of the Oxidation State of Pb on the Superconducting Transition Temperature of Bi2 – x Pb x Sr2CaCu2O8 + δ

A procedure is developed for determining the Pb⁴⁺ concentration in Pb-substituted Bi-based 2212 superconductors. The effect of the Pb⁴⁺ : Pb²⁺ ratio on the superconducting transition temperature of 2212 is studied. The results indicate that the highest T _c is offered by Bi_1.8Pb_0.2Sr₂CaCu₂O_{8 +} containing the smallest amounts of Pb and Cu in their higher oxidation states.     

A and B Phases Nucleation at a Fast Superfluid Transition in 3He. Can It Be Relevant for Cosmology ?

We discuss the extension of the Kibble-Zurek scenario of defects creation at cosmological phase transitions to the case when alternative symmetries may be broken and different states nucleated independently. We have calculated the nucleation probability of the various states of superfluid ³ He during a superfluid transition. Our results can explain the asymmetry of transition between non equilibrium A and B phases, triggered by nuclear reaction. The new scenario is a possible alternative to the well-known baked Alaska scenario. This scenario may also be relevant for the early universe, where two different states, SU(3) × SU(2) × U(1) and SU(4) × U(1) can be nucleated after the transition from SU(5) state.     

Visibility of the Aharonov–Bohm Effect in a Ring Coupled to a Fluctuating Magnetic Flux

We consider the visibility of the Aharonov–Bohm effect for cotunneling transport through a clean one-channel ring coupled to a fluctuating magnetic flux. We concentrate on the modification of the destructive interference at ₀ /2 by the fluctuating flux, since changes in the magnitude of the current away from this point can also be caused by renormalization effects and do not necessarily indicate dephasing. For fluctuations arising from the Nyquist noise in an external coil at T=0, the suppression of the destructive interference shows up only in a contribution proportional to V ³ , and therefore does not affect the linear conductance. In this sense, the Nyquist bath does not lead to dephasing in the linear transport regime at zero temperature in our model.     

A Method to Increase the Lateral Reversible Region of Bulk YBCO Above a Permanent Magnet Guideway

Lateral reversible region of the bulk high-T _c superconductor (HTSC) above the permanent magnet guideway (PMG) is a key parameter for the high-T _c superconducting (HTS) maglev system. The lateral stability and guidance force are proportional to the width of the lateral reversible region. When the lateral displacement of the bulk HTSC exceeds the reversible region, the maglev system will return to a new lateral equilibrium position. The method with the use of pre-displacement can successfully increases the lateral reversible region of the bulk HTSC. By the correct choice of the maximum lateral offset and a new starting point, the instability of flux motion can be suppressed. Unsuitable usage of this method will cause the intersection of guidance force and reduce the reversible region. Analyses based on the magnetizing history and pinning metamorphoses well explain the experimental results. Difference between this method and the pre-load method is also discussed in this article.     

Is the Tendency to Variation a Chief Cause of Progress?

This paper briefly reviews the sources of the diversity of innovativeactivity within industries, and interprets the literature tosuggest that there are three ways in which such diversity maystimulate technological progress, including a selection effect,a breadth effect and a complementarity effect. Using industry-leveldata from the Yale survey administered in the 1980s, the paperpresents preliminary empirical results on the relationship betweenthe diversity of R&D activities within industries and theirrate of technical advance. This exploratory exercise finds that,controlling for industry R&D intensity, greater diversityin innovative activity is associated with a more rapid paceof technological change. Policy implications are considered.     

Excitation of Narrow‐Band Pulsations in a Short Portion of Transition from the Smaller Diameter of a Pipe to a Larger Diameter and Possibilities of Preventing Them

By using models of the portions of the circuit of main gascompressor stations, data on the frequencies of narrowband pressure pulsations have been obtained; these data demonstrate the jet character of flow in divergent channels with angles of opening on one side of 12°47 and 23°50. It has been shown that narrowband acoustic disturbances are generated in the internal flow with largescale hydrodynamic structures. Intense narrowband pulsations are prevented by a grid of internal divergent channels in the transition portion with small angles of opening in canals and in excitation of certain disturbances upstream of a short divergent channel.     

The Calculation of an?Air Gap Between Pancake Windings in?a?Superconducting Magnet by Using the Response Surface Method

The effects of a gap at a high temperature superconducting magnet which has an insert magnet and an outsert magnet are examined. Both magnets consist of pancake windings. The optimum gap of an insert magnet and an outsert magnet are calculated by using the response surface method. The insert magnet consists of 8 YBCO pancake windings. The number of turns of a pancake winding and the inner diameter of the insert magnet are 60 turns and 40 mm, respectively. The outsert magnet consists of 12 BSCCO-2223 pancake windings. The number of turns of a pancake winding and the inner diameter of the outsert magnet are 100 turns and 115 mm, respectively. The calculation results show the optimum gap of the insert magnet and the outsert magnet are 0 and 10.3 mm, respectively. When there is a gap of 10.3 mm in the outsert magnet the central magnetic field increased by 11.4% from 604.2 to 542.6 mT. RSM is proved to be an effective mean for finding optimum gaps in a shorter time comparing with other non-deterministic optimization technique.     

The “Composite Polarons” Interesting Objects in the Physics of the Superconducting Materials?

We generalize the Landau Pekar theory of polarons by taking account of the screening of the Coulomb interactions, and of the coupling of the electrons with the acoustical phonons. We give a criterium of existence of polarons in the presence of screening. This criterium is probably not satisfied in metals, but it can be in anisotropic materials like the cuprates. Moreover, the composite polarons may attract each other at large distance. Finally, the screening lowers significantly the effective mass of the polarons.     

Can Masks Be Reused After Hot Water Decontamination During the COVID-19 Pandemic?

Masks have become one of the most indispensable pieces of personal protective equipment and are important strategic products during the coronavirus disease 2019 (COVID-19) pandemic. Due to the huge mask demand–supply gap all over the world, the development of user-friendly technologies and methods is urgently needed to effectively extend the service time of masks. In this article, we report a very simple approach for the decontamination of masks for multiple reuse during the COVID-19 pandemic. Used masks were soaked in hot water at a temperature greater than 56 °C for 30 min, based on a recommended method to kill COVID-19 virus by the National Health Commission of the People’s Republic of China. The masks were then dried using an ordinary household hair dryer to recharge the masks with electrostatic charge to recover their filtration function (the so-called “hot water decontamination + charge regeneration” method). Three kinds of typical masks (disposable medical masks, surgical masks, and KN95-grade masks) were treated and tested. The filtration efficiencies of the regenerated masks were almost maintained and met the requirements of the respective standards. These findings should have important implications for the reuse of polypropylene masks during the COVID-19 pandemic. The performance evolution of masks during human wear was further studied, and a company (Zhejiang Runtu Co., Ltd.) applied this method to enable their workers to extend the use of masks. Mask use at the company was reduced from one mask per day per person to one mask every three days per person, and 122 500 masks were saved during the period from 20 February to 30 March 2020. Furthermore, a new method for detection of faulty masks based on the penetrant inspection of fluorescent nanoparticles was established, which may provide scientific guidance and technical methods for the future development of reusable masks, structural optimization, and the formulation of comprehensive performance evaluation standards.     

National Standard Prepared to Be Established for the Field of Digitized Architecture

Thedigitalinformationtechnologyhasbecometheconsecutivelydevelopedchannelofthethicklydottedhighbuildingsandlargemansions.Recently,theNationalStandardCompilationCommitteeforDigitalTechnologyApplicationinConstructionandResidentialcommunitywasfoundedinBeijingtoensurethesounddevelopmentofthedigitalchannelinthefieldofthearchitecture,andthepreparationsfortherelatednation-alstandardwasstarted. TheprojectwasapprovedbytheStandardizationAd-ministrationofChina,organizedbytheMinistryofConstruction,…     

Can Twitter increase the visibility of Chinese publications?

Scientometrics - The purpose of this study is to investigate whether diffusion through social media can help to improve the international visibility of Chinese papers and thus increase their...     

Serve the Society with Standards to Create a Beautiful Life--＂User Oriented＂ Standards Concept to Boost Haier Development

Haier Group has always been plowing in the area of technical standards and committing itself to providing high-quality solutions to global consumers,to achieve a win-win situation between the enterprises and the users.     

Natural Fullerenes-Will they Offer a Hint to the Selective Synthesis of Fullerenes?

Abstract

In addition to the known laboratory methods of preparing fullerenes, which generally start from carbon vapor, studies of naturally occurring C₆₀/C₇₀ suggest a catalytic process of fullerene formation that proceeds in solid phase under mild condition. Recent observation of C₆₀/C₇₀ in Yunnan coal and Kalerian C-rich rock is reviewed in the light of the above perspective.     

Natural Fullerenes-Will they Offer a Hint to the Selective Synthesis of Fullerenes?

In addition to the known laboratory methods of preparing fullerenes, which generally start from carbon vapor, studies of naturally occurring C₆₀/C₇₀ suggest a catalytic process of fullerene formation that proceeds in solid phase under mild condition. Recent observation of C₆₀/C₇₀ in Yunnan coal and Kalerian C-rich rock is reviewed in the light of the above perspective.     

Effect of Te addition on some physical properties of the Se3S2 system and a study of the response to γ-irradiation

Glasses based on sulphur and tellurium were carefully characterized to establish the interdependence between chemical composition and the magnitudes of the physical parameters related to their use as infrared optical materials. Parameters considered in this paper are density, molar volume, transition temperatures, crystallization activation energy, decomposition energy, direct current (d.c.) electrical properties, optical energy gap and infrared transmission spectra in the range 400–6000 cm^–1. The irradiation has no detectable effect on both the d.c. conductivity of the bulk glass and the optical energy gap.     

Effect of Carbon on the Paramagnetic-Antiferromagnetic Transition and γ→εMartensitic Transformation of Fe-24Mn Alloys

1. IntroductionAlloying is the main approach to develop Fe-Mnbased alloy. FOr example, the improvement of theoxidation-resistant and corrosion-resistant propertiesby adding Cr in Fe-Mn alloy leads to the development of Fe-Mn-Cr heat-resistant alloy, stainless steeland non--magnetic steel. The Fe-Mn-Al cryogenic andnon-magnetic steels were developed due to the strongdepressing effect of Al on the 7~e martensitic transformation in Fe-Mn alloy. St is another interesting example for its rema…     

Strong Vortex Pinning in the Low–Temperature Superconducting Phase of (U1−xThx)Be13

We have found a sharp transition at T _c2 = 350 mK in the vortex creep rate of a single crystal of (U _1–x Th _x )Be ₁₃ with T _c = 523 mK (x = 0.0275). For T T _c2 , no creep of vortices is observed in a time scale of 10⁵ s, while for T _c2 < T < T _c , vortices creep at very high rates (30% of decay from a metastable configuration in the first 10⁵ s at T = 400 mK). The sharp transition occurs at the same temperature at which the second jump in the specific heat appears in these samples. Similar low levels of creep rates have been reported by us in the low–T superconducting phase of UPt ₃.¹