When should we change the definition of the second?

The microwave caesium (Cs) atomic clock has formed an enduring basis for the second in the International System of Units (SI) over the last few decades. The advent of laser cooling has underpinned the development of cold Cs fountain clocks, which now achieve frequency uncertainties of approximately 5×10(-16). Since 2000, optical atomic clock research has quickened considerably, and now challenges Cs fountain clock performance. This has been suitably shown by recent results for the aluminium Al(+) quantum logic clock, where a fractional frequency inaccuracy below 10(-17) has been reported. A number of optical clock systems now achieve or exceed the performance of the Cs fountain primary standards used to realize the SI second, raising the issues of whether, how and when to redefine it. Optical clocks comprise frequency-stabilized lasers probing very weak absorptions either in a single cold ion confined in an electromagnetic trap or in an ensemble of cold atoms trapped within an optical lattice. In both cases, different species are under consideration as possible redefinition candidates. In this paper, I consider options for redefinition, contrast the performance of various trapped ion and optical lattice systems, and point to potential limiting environmental factors, such as magnetic, electric and light fields, collisions and gravity, together with the challenge of making remote comparisons of optical frequencies between standards laboratories worldwide.     

On the shoulders of students? The contribution of PhD students to the advancement of knowledge

Using the participation in peer reviewed publications of all doctoral students in Quebec over the 2000–2007 period, this paper provides the first large scale analysis of their research effort. It shows that PhD students contribute to about a third of the publication output of the province, with doctoral students in the natural and medical sciences being present in a higher proportion of papers published than their colleagues of the social sciences and humanities. Collaboration is an important component of this socialization: disciplines in which student collaboration is higher are also those in which doctoral students are the most involved in peer-reviewed publications. In terms of scientific impact, papers co-signed by doctorate students obtain significantly lower citation rates than other Quebec papers, except in natural sciences and engineering. Finally, this paper shows that involving doctoral students in publications is positively linked with degree completion and ulterior career in research.     

Is the proton radius a player in the redefinition of the International System of Units?

It is now recognized that the International System of Units (SI units) will be redefined in terms of fundamental constants, even if the date when this will occur is still under debate. Actually, the best estimate of fundamental constant values is given by a least-squares adjustment, carried out under the auspices of the Committee on Data for Science and Technology (CODATA) Task Group on Fundamental Constants. This adjustment provides a significant measure of the correctness and overall consistency of the basic theories and experimental methods of physics using the values of the constants obtained from widely differing experiments. The physical theories that underlie this adjustment are assumed to be valid, such as quantum electrodynamics (QED). Testing QED, one of the most precise theories is the aim of many accurate experiments. The calculations and the corresponding experiments can be carried out either on a boundless system, such as the electron magnetic moment anomaly, or on a bound system, such as atomic hydrogen. The value of fundamental constants can be deduced from the comparison of theory and experiment. For example, using QED calculations, the value of the fine structure constant given by the CODATA is mainly inferred from the measurement of the electron magnetic moment anomaly carried out by Gabrielse's group. (Hanneke et al. 2008 Phys. Rev. Lett. 100, 120801) The value of the Rydberg constant is known from two-photon spectroscopy of hydrogen combined with accurate theoretical quantities. The Rydberg constant, determined by the comparison of theory and experiment using atomic hydrogen, is known with a relative uncertainty of 6.6×10(-12). It is one of the most accurate fundamental constants to date. A careful analysis shows that knowledge of the electrical size of the proton is nowadays a limitation in this comparison. The aim of muonic hydrogen spectroscopy was to obtain an accurate value of the proton charge radius. However, the value deduced from this experiment contradicts other less accurate determinations. This problem is known as the proton radius puzzle. This new determination of the proton radius may affect the value of the Rydberg constant . This constant is related to many fundamental constants; in particular, links the two possible ways proposed for the redefinition of the kilogram, the Avogadro constant N(A) and the Planck constant h. However, the current relative uncertainty on the experimental determinations of N(A) or h is three orders of magnitude larger than the 'possible' shift of the Rydberg constant, which may be shown by the new value of the size of the proton radius determined from muonic hydrogen. The proton radius puzzle will not interfere in the redefinition of the kilogram. After a short introduction to the properties of the proton, we will describe the muonic hydrogen experiment. There is intense theoretical activity as a result of our observation. A brief summary of possible theoretical explanations at the date of writing of the paper will be given. The contribution of the proton radius puzzle to the redefinition of SI-based units will then be examined.     

How different are the indicatrixes of the leaves of various woody plant species?

Some researchers assume that the light reflection from leaves is Lambertian, but I verify that some leaves exist showing no Lambertian reflection. One can measure the indicatrixes of leaves of various woody plant species by the use of a goniophotometer. Minnaert constants can be calculated from these indicatrixes for quantitative evaluation. I discuss why light scattering from leaves does not always obey Lambertian law.     

Optimization of composite patch repair processes with?the?use of genetic algorithms

The aim of this contribution is the optimization of some parameters of the composite patch repair technique (CPR). This technique is mainly used by the aircraft industry, as it offers high reliability, short repair times and reduced cost in compare to other methods, such as the riveted joints. CPR consists of adhesively bonding thin composite patches over cracked or corroded areas with heat supply. As the polymer-matrix composite patch is heated, it cures and toughens. Proper curing insures structural reliability of the repair. Short duration curing cycles are of great importance for the aircraft availability. With the use of Genetic Algorithms, we design minimum time curing cycles. The optimization is subjected to the following constraints: (1) Maximum allowed temperature in order to avoid residual stresses, (2) Minimum temperature in order to initiate the cure reaction, (3) Sufficient degree of cure at the end of the process and (4) Maximum heat generation rate that can be achieved by the device. Our design vector contains the duration of the plateau stage of the cure cycle and the characteristic thermal profile. The degree of cure is estimated with the use of the Kamal cure rate model for thermosetting polymers. For the numerical time integration of the cure rate equation, a second order, implicit Runge-Kutta scheme is employed.     

Does the multi-authorship trend influence the quality of an article?

In the last few decades, multi-authored articles have increased in different disciplines with increasing instances of authorship abuse although multi-authorship is not always due to undeserving authorship (McDonald et al. in Mayo Clin Proc 85(10):920–927, 2010). It may be necessitated by interdisciplinary research, the evolution of a discipline, or the intention of quality improvement. This article studies the relationship between the authorship and the quality of articles (publications in better impact factor journals or core journals) in the field of Oceanography. The result shows ~75 % increase in the number of authors per article from 1990 to 2009 in the discipline. The increase in authorship correlates not only with the percentage of articles in core journals but also with the mean impact factor (IF) of journals (where the articles were published). The ANOVA study shows that though multi-authorship has no influence on the preference to publish in core journals during the 1990s or 2000s, it does have a significant influence on the preference to publish in high IF journals in both the decades. So these findings establish that in the field of Oceanography, the increase in collaboration would have resulted in more publications in core journals (without any influence of authorship increase) and in better impact factor journals (due to the influence of authorship increase).     

Abnormal Behavior of the Angular Dependence of Resistivity in?YBCO?Thin Films

Careful investigation of the angular dependence of resistivity ??(??) (?? is the angle between the magnetic field and the ab-planes) as a function of the temperature within the superconducting transition in an applied magnetic field B up to 1 T for a series of YBa₂Cu₃O_7??? (YBCO) thin films revealed a large variation in the shape and width of the minimum displayed in the vicinity of ??=0??, from a flat to a very sharp behavior. The series of films studied included both optimally doped and underdoped samples of different T _c , critical current density?J _c , film thickness, and preparation techniques. ??(??) measured for B close to ??=0?? (B parallel to ab-planes) for both B??J and B??J (J is the applied current density) showed two classes of samples; class of samples where ??(??) is independent of the direction of B relative to J and the other class where ??(??) depends on the orientation B relative to?J. This unusual unique behavior motivated us to investigate its origin by looking at the scaling of ??(??) as a function of the reduced field. Scaling of ??(??)) with the reduced field B(?? ^?2cos?² ??+sin?²)^1/2 allowed a quantitative determination of the value of ?? (intrinsic anisotropy) which varies between 7 and 400, and is independent of film thickness and J _c . Analysis of the microstructure though XRD of the films studied showed that the anisotropy is related to microstrain of the films.     

Is the time-dependent behaviour of the aortic valve intrinsically quasi-linear?

The widely popular quasi-linear viscoelasticity (QLV) theory has been employed extensively in the literature for characterising the time-dependent behaviour of many biological tissues, including the aortic valve (AV). However, in contrast to other tissues, application of QLV to AV data has been met with varying success, with studies reporting discrepancies in the values of the associated quantified parameters for data collected from different timescales in experiments. Furthermore, some studies investigating the stress-relaxation phenomenon in valvular tissues have suggested discrete relaxation spectra, as an alternative to the continuous spectrum proposed by the QLV. These indications put forward a more fundamental question: Is the time-dependent behaviour of the aortic valve intrinsically quasi-linear? In other words, can the inherent characteristics of the tissue that govern its biomechanical behaviour facilitate a quasi-linear time-dependent behaviour? This paper attempts to address these questions by presenting a mathematical analysis to derive the expressions for the stress-relaxation G(t) and creep J(t) functions for the AV tissue within the QLV theory. The principal inherent characteristic of the tissue is incorporated into the QLV formulation in the form of the well-established gradual fibre recruitment model, and the corresponding expressions for G(t) and J(t) are derived. The outcomes indicate that the resulting stress-relaxation and creep functions do not appear to voluntarily follow the observed experimental trends reported in previous studies. These results highlight that the time-dependent behaviour of the AV may not be quasi-linear, and more suitable theoretical criteria and models may be required to explain the phenomenon based on tissue’s microstructure, and for more accurate estimation of the associated material parameters. In general, these results may further be applicable to other planar soft tissues of the same class, i.e. with the same representation for fibre recruitment mechanism and discrete time-dependent spectra.     

Does hemodiafiltration improve the removal of homocysteine?

High prevalence of hyperhomocysteinemia is common in hemodialysis (HD) patients and could contribute to worsen the cardiovascular risk. Beyond vitamin B status, dialysis modality itself could influence homocysteine (Hcy) levels. The objective was compare the reduction rate (RR) of Hcy and cysteine in stable dialyzed patients treated by standard HD or hemodiafiltration (HDF). Seventy‐five patients undergoing stable dialysis through standard high‐flux HD (n = 35) or HDF (n = 40) were included. Biological parameters were determined before and after a midweek dialysis session. Urea percent reduction per session and Kt/V index (K, body urea clearance, T, time of dialysis, and V, urea distribution volume), defined as a marker of dialysis efficacy, were similar between HD and HDF groups. By contrast, higher RR of beta2 microglobulin (β2m) was observed in HDF compared with HD (78.6 vs. 72.0%, respectively; P < 0.001). Likewise, higher RR of Hcy was obtained with HDF compared to HD (46.0 vs. 41.5%, respectively; P < 0.05), whereas the RR of cysteine was similar in both groups. Interestingly, a positive correlation between Hcy RR and urea Kt/V index was observed (r = 0.29, P < 0.05) and between Hcy RR and β2m RR (r = 0.45, P < 0.001). Time‐averaged concentration (TAC) of Hcy was lower with HDF compared with HD (17.8 vs. 19.1 μmol/L, respectively), although not significant. There was no difference in median Hcy according to dialysis modality for neither pre‐ nor postdialysis levels. Significant higher removal of Hcy was observed with HDF compared with standard HD, although urea Kt/V index was similar. Enhanced removal of middle molecules, such as β2m, could be involved in Hcy RR improvement with HDF.     

No free lunches in nature? An analysis of the regional distribution of the affiliations of Nature publications

Nature is among the world’s most highly cited multidisciplinary science journals with one of the highest impact factors of 38.597 (Nature Publishing Group (NPG) 2013), which is used relatively often in many scientific rankings. When analysing the regional distribution of Nature publications, we found a high correlation between the expenditures and the number of local affiliations that are counted on a national basis. The same regularity can be observed for the world’s top 30 and the US’s top 50 universities; however, the correlation is now skewed by the so-called cumulative advantage or the Matthew Effect, which evidently rewards those that are ranked at the top of the Academic Ranking of World Universities. The rich get richer and the poor get poorer. Surprisingly, the amount of the endowment better determines the number of Nature publications for universities than the total research expenditure.     

On the Freezing and Melting Behavior of the Eutectic Pt?CC

The feasibility of referring to freezing as an alternative to melting for defining the eutectic transition temperature has been studied using two Pt?CC cells constructed at NIM, one of a sleeve type, and the other of a hybrid type, including support. Freezing and melting experiments have been done by varying the offset of the furnace temperature T _furn with respect to the nominal eutectic temperature T _E used to freeze the fixed point with offsets (T _furn?T _E)_freeze from ?5 K to ?40 K, followed by melting at a fixed offset (T _furn?T _E)_melt =?+?20 K. Plotting the liquidus temperatures T _liq,freeze and T _liq,melt obtained for freezing and melting against ${(T_{\rm E}-T_{\rm furn})^{1/2}_{\rm freeze}}$ resulted in linear relations for both cells, allowing extrapolation toward T _liq,freeze(0) and T _{liq, melt}(0). For the cells Pt?CC5# and Pt?CC6# under study: T _liq,melt(0)?T _liq,freeze(0) =?10 mK and 20 mK, respectively, with a standard uncertainty of 30 mK for both T _liq,melt(0) and T _liq,freeze(0). The coherence of the results obtained for melting and freezing indicates that freezing can be used, as an alternative to melting, to define the liquidus temperature T _liq(0) of the eutectic Pt?CC.     

Influence of Diffusion-Annealing Temperature on?the?Physico-Mechanical Properties of Au-doped Bi-2223 Superconductors

In order to investigate the influence of Au doping and diffusion-annealing temperature on the mechanical and superconducting properties of Bi-2223, Bi_1.8Pb_0.35Sr_1.9Ca_2.1Cu₃O _y superconductors were prepared by standard solid-state reaction methods. Doping of Bi-2223 was carried out by means of gold diffusion during sintering from an evaporated gold film on pellets. The investigation consisted of scanning electron microscopy, dc resistivity and hardness measurements. Electrical-resistivity measurements indicated that the room-temperature resistivity value decreased with decreasing diffusion-annealing temperature from 830 to 500?°C and these samples (G830, G800, G750, G700, G600 and G500) show the resistive behavior above the onset critical transition temperature with the zero-resistivity transition temperatures of 104 K, 80 K, 98 K, 95 K, 102 K and 103 K, respectively. To investigate mechanical properties of the samples, we have measured the diagonal length as a function of test load in the range of 0.245?C2.940 N. Mechanical properties (microhardness, Young??s modulus, yield strength and fracture toughness) of the samples are found to be load and diffusion-annealing temperature dependent. In addition, we have calculated the load independent hardness, Young??s modulus, yield strength, and fracture toughness of the samples. The possible reasons for the observed changes in superconducting and mechanical properties due to Au diffusion and diffusion-annealing temperature were discussed.     

Research or management? An investigation of the impact of leadership roles on the research performance of academic administrators

This study quantitatively investigated whether the research performance of academic administrators (leaders) was affected by their administrative services. We sampled 111 academic administrators, including 90 department deans and 21 university presidents, from 26 universities. These leaders’ research performance was determined by the number of their publications and citations in the Web of Science databases. To compare the effect on their research performance by their administrative roles, we proposed four periods: the pre-position period, the latest position period, the reference period, and the in-position period. Statistical methods were applied to compare the research performance of the sampled administrators before and after they accepted the current administrative roles. The results suggest that 80% of academic leaders’ productivity and citation have fallen by 42 and 62% averagely. The extent of such impact varied in different disciplines. Leaders’ performance in medicine fields has declined the most (60%). The impact on research productivity appeared to be stronger for administrators serving in higher-ranking universities. In addition, the research performance of both university presidents and department deans were substantially influenced by their administrative services.