Dynamic inversion of planar-chiral response of terahertz metasurface based on critical transition of checkerboard structures

Dynamic inversion of the planar-chiral responses of a metasurface is experimentally demonstrated in the terahertz regime. To realize this inversion, the critical transition of the checkerboard-like metallic structures is used. Resonant structures with planar chirality and their complementary enantiomeric patterns are embedded in the checkerboard. Using vanadium dioxide as a variable resistance, the metasurface is implemented in the terahertz regime. The responses of the metasurface to circularly polarized waves are then characterized by terahertz time-domain spectroscopy. Further, the sign of the circular conversion dichroism, which is closely related to the handedness of the planar chirality of the metasurface, is observed to be inverted at 0.64 THz by varying the temperature. Such invertible planar-chiral responses can be applied practically to the handedness-invertible chiral mirrors.

Study on the Relationship between Uniaxial Strain and Critical Transition Temperature of MgB2 Based on First-principles

It has been shown that the critical transition temperature (Tc) of MgB2 superconducting materials decreases with the increase of hydrostatic pressure, but this is a comprehensive Tc change after multiaxial strain, and the influence of strain on Tc is not clearly understood. In this paper, based on the McMillan superconducting calculation formula and the first-principles density functional theory, the Tc change of MgB2 under uniaxial strain and the properties of MgB2 such as energy band, Fermi surface, differential charge density and phonon dispersion spectrum under uniaxial strain are studied, and the relationship between uniaxial strain and these properties is analyzed. The calculated Tc of MgB2 at zero strain is 38.35 K, which is in good agreement with the experimental value of 39 K. When the a-axis strain is 1%, the Tc value can be increased to 49.7 K, and there is a further improvement trend. When the a-axis compression strain is -1%, Tc decreases to 31.52 K. When the c-axis tensioncompression strain is applied, the change of Tc value is small. Further analysis shows that the influence of a-axis strain on the differential charge density, electronic band structure, phonon dispersion and other properties of MgB2 is significantly greater than that of c-axis strain, and the influence of these properties on Tc is discussed. The work in this paper has certain theoretical and guiding significance for the preparation of MgB2 with higher Tc and the study of the effect of uniaxial strain on Tc of superconducting materials.

Critical transition to a non-chaotic regime in isotropic turbulence

We study the properties of homogeneous and isotropic turbulence in higher spatial dimensions through the lens of chaos and predictability using numerical simulations. We employ both direct numerical simulations and numerical calculations of the eddy damped quasi-normal Markovian closure approximation. Our closure results show a remarkable transition to a non-chaotic regime above the critical dimension, $d_c$ , which is found to be approximately 5.88. We relate these results to the properties of the energy cascade as a function of spatial dimension in the context of the idea of a critical dimension for turbulence where Kolmogorov's 1941 theory becomes exact.

Impact of Lockdown for Researchers

The book on "Impact of Lockdown for Researchers" is a very good effort in bringing novel ideas at the time of the pandemic. The engagement with the research community leading to this wonderful outcome is laudable. As the editors of this book, we are fortunate to go through every article and found few interesting impacts of lockdown in researchers career. Congratulations and wishes to authors and publishers for bringing out this productive outcome in the most critical transition time of this pandemic.

Landscape dynamic network biomarker analysis reveals the tipping point of transcriptome reprogramming to prevent skin photodamage

Skin, as the outmost layer of human body, is frequently exposed to environmental stressors including pollutants and ultraviolet (UV), which could lead to skin disorders. Generally, skin response process to ultraviolet B (UVB) irradiation is a nonlinear dynamic process, with unknown underlying molecular mechanism of critical transition. Here, the landscape dynamic network biomarker (l-DNB) analysis of time series transcriptome data on 3D skin model was conducted to reveal the complicated process of skin response to UV irradiation at both molecular and network levels. The advanced l-DNB analysis approach showed that: (i) there was a tipping point before critical transition state during pigmentation process, validated by 3D skin model; (ii) 13 core DNB genes were identified to detect the tipping point as a network biomarker, supported by computational assessment; (iii) core DNB genes such as COL7A1 and CTNNB1 can effectively predict skin lightening, validated by independent human skin data. Overall, this study provides new insights for skin response to repetitive UVB irradiation, including dynamic pathway pattern, bi-phasic response, and DNBs for skin lightening change, and enables us to further understand the skin resilience process after external stress.

Improving how schools engage families during the crucial 9th-grade year

Researchers Martha Abele Mac Iver, Joyce Epstein, and Steven Sheldon summarize the outcomes of their four-year partnership with an urban district aimed at improving the ways schools engage families during the critical transition to high school. They describe how schools put into practice the strategies learned in ongoing professional development, how family engagement practices changed, and what effects those changes had on students. Particular strategies include the use of an online parent portal and interactive homework assignments about the transition to high school.

The hybrid scale factor, the transition from the matter dominated era to the dark energy dominated era and time evolution of the Universe

The late time crossover from matter dominated era (represented power-law evolution) to the dark energy dominated era (represented exponential evolution) of the Universe evolution is the major problem in today’s physical cosmology. Unless this critical transition problem is solved, it is not possible to reach a holistic theory of cosmology. To explain this critical transition we propose a new model where the dark matter and dark energy interacting through a potential. Based on the FLRW framework we analytically solve this model and obtain the scale factor a(t). In addition, we numerically compute all cosmological quantities. We find more significant results to enlightening the physical mechanism of the critical transition. Firstly, we show that the scale factor a(t) has a hybrid form as a(t) = a0(t/t0) α e ht/t0 . This is main and important result in the presented work, which clearly indicates that the transition from the power-law to the exponential expansion of the Universe. The numerical results clearly provide that there is a time crossover tc in the scale factor a curve, which indicates the transition from the power-law to the exponential expansion of the Universe. Below t/t0 ≤ tc, matter era dominated hence time evolution of the Universe is given by a(t) ∝ (t/t0) α , on the other hand, above t/t0 > tc, the evolution is represented by a(t) ∝ exp(ht/t0). It is first time, the hybrid result for scale factor is exactly obtained from the presented model without use any approximation. Secondly, we fit the scale factor below and above tc. Surprisingly, we find that the scale factor behaves as a(t) ∝ (t/t0) 2/3 below t/t0 ≤ tc, and as a(t) ∝ exp(ht/t0) which indicates that the Hubble parameter takes the value in the interval of the around H0 = 69.5 and H0 = 73.5 km s−1Mpc−1 depend on the weak and strong interactions between dark components above t/t0 > tc, respectively. These are remarkable that α = 2/3 is completely consistent exact solution of the FLRW and re-scaled Hubble parameter H0 is the observable intervals given by Planck, CMB and SNIa data (or other combinations) for chosen interaction values are purely consistent with cosmological observations. Thirdly, we find from the model the transition point from matter dominated era to the dark energy dominated era in the cosmic time is the t0 = 9.8 Gyear which is consistent with the theoretical solution and observations. Additionally, we numerically obtain and analyse other cosmological quantities such as dimensionless Hubble parameter h, deceleration parameter q, jerk parameter j and EoS parameter w. We show that all cosmological quantities of this model are consistent observational results for the matter and dark energy dominated eras. As a result, we consider late time crossover of the Universe, we propose an interacting dark matter and dark energy model, we show that this model can explain the late time crossover phenomena of the Universe and our solutions are very good consistent with theoretical and observational results. Finally, we state that this work makes essential steps towards solving a critical outstanding problem of the cosmology, and has a potential to creates a paradigm for future studies in this field. Furthermore, the model also sheds light on the interaction mechanism of dark matter and dark energy in the Universe.

Society and the moral semantics of the COVID-19 pandemic: a social systems approach

PurposeIn a context of critical transition such as the COVID-19 pandemic, moral semantics take a prominent role as a form of self-description of society. However, they are not usually observed, but rather assumed as self-evident and necessarily “good.” The purpose of the article is to summarize the theory of morality from the social systems' perspective and illustrate with concrete examples the polemogenous nature of moral communication.Design/methodology/approachThis article presents an analysis of the role of morality in the context of the COVID-19 pandemic, from the perspective of Niklas Luhmann’s social systems theory. Applying the method of second-order observation, it describes three cases of moral semantics disseminated via mass media and social media, and it examines their connection with the structural situation of subsystems of society during the pandemic crisis (particularly healthcare, politics and science).FindingsSecond-order observation of moral communication demonstrates to be fruitful to describe the conditions and consequences in which moralization of communication occurs, particularly in a situation of critical transition around the healthcare crisis. The three examples examined, namely, the hero semantics directed to healthcare workers, the semantics of indiscipline and the controversies around pseudo-sciences and conspiracy theories, show how they are based on social attribution of esteem and disesteem, how they try to answer to troublesome situations and contradictions that seem difficult to cope, and how they are close related to the emergence of conflicts, even when they seem positive oriented and well intentioned.Originality/valueThis paper is an attempt to test the usefulness of Luhmann's theory of society to understand the ongoing COVID-19 crisis and particularly the role of moral communication in concrete examples.

Catching Critical Transition in Engineered Systems

A variety of engineered systems can encounter critical transitions where the system suddenly shifts from one stable state to another at a critical threshold. The critical transition has aroused vital concerns for its potentially disastrous impacts. We validate an often taken-for-granted hypothesis that the failure of engineered systems can be attributed to the respective critical transitions and show how early warning signals are closely associated with critical transitions. We demonstrate that it is feasible to use early warning signals to predict system failures. Our findings open a new path to forecast failures of engineered systems with a generic method and provide supporting evidence for the universal existence of critical transition in dynamical systems at multiple scales.