In this paper we present the efficient design of functional thin-film metamaterial devices with the effective surface conductivity approach. As an example, we demonstrate a graphene based perfect ...absorber. After formulating the requirements to the perfect absorber in terms of surface conductivity we investigate the properties of graphene wire medium and graphene fishnet metamaterials and demonstrate both narrowband and broadband tunable absorbers.
Exploiting a template effect of 1,4-diazacycloheptane (also known as homopiperazine, Hpipe), four new hybrid iodides, (HpipeH
)
Bi
I
·2H
O, (HpipeH
)I(I
), (HpipeH
)
I
·H
O, and (HpipeH
)
(H
O)I
, ...were prepared and their crystal structures were solved using single crystal X-ray diffraction data. All four solid-state crystal structures feature the HpipeH
cation alternating with Bi
I
, I
, or I
anions and solvent water or H
O
cation. HpipeH
assembles anionic and neutral building blocks into polymer structures by forming four strong (N)H···I and (N)H···O hydrogen bonds per cation, with the H···I distances ranging from 2.44 to 2.93 Å and H···O distances of 1.88-1.89 Å. These hydrogen bonds strongly affect the properties of compounds; in particular, in the case of (HpipeH
)
Bi
I
·2H
O, they ensure narrowing of the band gap down to 1.8 eV and provide high thermal stability up to 240 °C, remarkable for a hydrated molecular solid.
Myopia occurs in more than 50% of the population in many industrialized countries and is expected to increase; complications associated with axial elongation from myopia are the sixth leading cause ...of blindness. Thus, understanding its etiology, epidemiology, and the results of various treatment regiments may modify current care and result in a reduction in morbidity from progressive myopia. This rapid increase cannot be explained by genetics alone. Current animal and human research demonstrates that myopia development is a result of the interplay between genetic and the environmental factors. The prevalence of myopia is higher in individuals whose both parents are myopic, suggesting that genetic factors are clearly involved in myopia development. At the same time, population studies suggest that development of myopia is associated with education and the amount time spent doing near work; hence, activities increase the exposure to optical blur. Recently, there has been an increase in efforts to slow the progression of myopia because of its relationship to the development of serious pathological conditions such as macular degeneration, retinal detachments, glaucoma, and cataracts. We reviewed meta-analysis and other of current treatments that include: atropine, progressive addition spectacle lenses, orthokeratology, and multifocal contact lenses.
A method for the local and global interpretation of a black-box model on the basis of the well-known generalized additive models is proposed. It can be viewed as an extension or a modification of the ...algorithm using the neural additive model. The method is based on using an ensemble of gradient boosting machines (GBMs) such that each GBM is learned on a single feature and produces a shape function of the feature. The ensemble is composed as a weighted sum of separate GBMs resulting a weighted sum of shape functions which form the generalized additive model. GBMs are built in parallel using randomized decision trees of depth 1, which provide a very simple architecture. Weights of GBMs as well as features are computed in each iteration of boosting by using the Lasso method and then updated by means of a specific smoothing procedure. In contrast to the neural additive model, the method provides weights of features in the explicit form, and it is simply trained. A lot of numerical experiments with an algorithm implementing the proposed method on synthetic and real datasets demonstrate its efficiency and properties for local and global interpretation.
The Sestrins constitute a family of evolutionarily conserved stress-inducible proteins that suppress oxidative stress and regulate AMP-dependent protein kinase (AMPK)-mammalian target of rapamycin ...(mTOR) signaling. By virtue of these activities, the Sestrins serve as important regulators of metabolic homeostasis. Accordingly, inactivation of Sestrin genes in invertebrates resulted in diverse metabolic pathologies, including oxidative damage, fat accumulation, mitochondrial dysfunction, and muscle degeneration, that resemble accelerated tissue aging. Likewise, Sestrin deficiencies in mice led to accelerated diabetic progression upon obesity. Further investigation of Sestrin function and regulation should provide new insights into age-associated metabolic diseases, such as diabetes, myopathies, and cancer.
The C–N cross-coupling chemistry intensely developed since the late 1990s has supplied synthesists with an overwhelming number of methods to effectively combine carbon and nitrogen residues. This new ...chemistry relies on complexes of mainly two metals, copper and palladium, used as catalysts or stoichiometric agents. The development of new methods has revealed both similarities and differences in the principles used for the design of new catalytic systems and analysis of their reactivity and selectivity. The discussion of cross-coupling chemistry of these two metals can be performed within a common mechanistic paradigm, helping to elucidate the key factors governing the behavior of the transition-metal complexes involved.
Mice deficient for SIRT6 exhibit a severely shortened lifespan, growth retardation, and highly elevated LINE1 (L1) activity. Here we report that SIRT6-deficient cells and tissues accumulate abundant ...cytoplasmic L1 cDNA, which triggers strong type I interferon response via activation of cGAS. Remarkably, nucleoside reverse-transcriptase inhibitors (NRTIs), which inhibit L1 retrotransposition, significantly improved health and lifespan of SIRT6 knockout mice and completely rescued type I interferon response. In tissue culture, inhibition of L1 with siRNA or NRTIs abrogated type I interferon response, in addition to a significant reduction of DNA damage markers. These results indicate that L1 activation contributes to the pathologies of SIRT6 knockout mice. Similarly, L1 transcription, cytoplasmic cDNA copy number, and type I interferons were elevated in the wild-type aged mice. As sterile inflammation is a hallmark of aging, we propose that modulating L1 activity may be an important strategy for attenuating age-related pathologies.
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•SIRT6 KO mice accumulate L1 cDNA, triggering interferon response via cGAS pathway•Wild-type aged mice accumulate L1 cDNA and display type I interferon response•Reverse-transcriptase inhibitors rescue type I interferon response and DNA damage•Reverse-transcriptase inhibitors extend lifespan and improve health of SIRT6 KO mice
Simon et al. show that LINE1 retrotransposon elements are derepressed in aged and progeroid mice. Cytoplasmic accumulation of LINE1 cDNA copies induced a type I interferon response, through the cGAS DNA sensing pathway, resulting in pathological inflammation. Inhibiting L1 replication significantly improved the health and lifespan of aged mice.
In this paper, a new wake oscillator model with nonlinear coupling is proposed for the modelling of vortex-induced vibration. The purpose is to develop a model that is capable of reproducing both ...free and forced vibration experiments. To achieve this goal, an existing van der Pol wake oscillator model is first reviewed. The limitations of the model are discussed and the influence of different drag force models on the dynamic characteristics of the fluctuating lift force that matches the forced vibration experiments are studied. Based on this model, nonlinear coupling terms are introduced to improve its predictive capabilities. The tuning of this improved model to the forced vibration shows a good agreement with experiments in terms of the added damping. However, the model failed to capture the negative added mass at high reduced velocities. As a result, the new model underpredicts both the range and frequency of lock-in in free vibration tests. To eliminate this discrepancy, the model is further enhanced by introducing frequency dependent nonlinear couplings, which are achieved in the time domain by means of convolution integrals. A single set of frequency dependent, complex-valued functions – which are the Laplace transforms of corresponding convolution kernels – that reproduce the forced vibration experiments is determined over a limited range of frequencies. However, no analytical extension of these functions to the infinite frequency domain was found such that the causality principle and the energy conservation would be satisfied. The latter is a major challenge for all existing wake oscillator models that aim at reproducing the forced vibration experiments.
We reveal an outstanding potential of water as an inexpensive, abundant and bio-friendly high-refractive-index material for creating tunable all-dielectric photonic structures and metamaterials. ...Specifically, we demonstrate thermal, mechanical and gravitational tunability of magnetic and electric resonances in a metamaterial consisting of periodically positioned water-filled reservoirs. The proposed water-based metamaterials can find applications not only as cheap and ecological microwave devices, but also in optical and terahertz metamaterials prototyping and educational lab equipment.
The problem of the size dependence of physical properties is one of the most intriguing when we transit to the nano-level. Experiments have shown that this effect is characteristic of the elastic ...modulus of many polymeric nanofibers obtained by electrospinning. Existing explanations of this effect did not offer a general understanding of the physical nature of this phenomenon. In this study, we propose a universal model of this phenomenon. We consider the structure of fibers within the framework of the core-shell model, in which the shell is approximated by a thin elastic surface. The analysis of deformation is based on the fundamental laws of the mechanics of deformation of twisted thin shells and, unlike the theories proposed earlier, does not require any additional artificial arguments. This approach made it possible to obtain a simple analytical expression for the size dependence of the elastic modulus, which represents it as the sum of the bulk modulus of the core and two additional moduli proportional to D-1 and D-3, respectively. The resulting model corresponds to all available (from published sources) experimental data, related to polymer of very different chemical structure, and therefore can be considered as universal.
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