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Adding isopropylamonium cation in quasi-2D perovskite films leads to a change in phase distribution and orientation of crystalline domains, with efficient sky blue emission. This allows the fabrication of LEDs with high luminescence and color purity.

Double perovskites Cs2Na1−xAgxIn1−yBiyCl6 can emit warm white light with almost unity quantum efficiency and are thus among the most promising materials for solid-state lighting. The emission spectrum is reproducible and the materials themselves are robust against degradation, as well as fabricated from earth-abundant, non-toxic precursors. The emission efficiency is however sensitive to the materials composition, with small variations modifying the photoluminescence quantum yield by more than an order of magnitude. We provide here a comprehensive, systematic study of the optical properties as a function of composition and identify the microscopic mechanism linking the presence of Bi and Ag to the high emission quantum yield. A 0.1% minimum fraction of Bi and Ag is found to trigger efficient emission of warm white light. Ag alloying is fundamental to obtain high emission yields. Continuous-wave spectroscopy measurements are complemented with ab initio computation of the electronic band structure in demonstrating that Bi strengthens optical absorption at the band gap edge of the double perovskites. In addition, it is found by combining time-resolved photoluminescence and transient absorption spectroscopy that Ag and Bi promote the formation of bright (radiative) self-trapped excitons, while inhibiting exciton relaxation into long-lived dark states.

Carl Schmitt’s critical insights into ‘economic-technical thinking’ and the dominant role that a ‘magical technicity’ is said to assume in the social horizon of his times offers an opportunity to reframe contemporary debates on political and economic theology, exposing a theological core behind technocratic administration. Starting from this premise, the article engages with recent inquiries into so-called ‘debt economy’, assessing the affective function that ‘deferment’ and ‘confession’ perform as dominant operators in the social imaginary of neoliberal governance.

Thin-rim gears are widely used in industrial fields such as aerospace and electric vehicles due to the advantage of light weight. Yet, the root crack fracture failure of thin-rim gears significantly limits their application and further affects the reliability and safety of high-end equipment. In this work, the root crack propagation behavior of thin-rim gears is experimentally and numerically investigated. The crack initiation position and crack propagation path for different backup ratio gears are simulated using gear finite element (FE) models. The crack initiation position is determined using the maximum gear root stress position. An extended FE method coupled with commercial software ABAQUS is used to simulate the gear root crack propagation. The simulation results are then verified by conducting experimental tests for different backup ratio gears based on a dedicated designed single-tooth bending test device.

The development of an environmentally friendly fabrication process for non-fullerene acceptor organic solar cells is an essential condition for their commercialization. However, devices fabricated by processing the active layer with green solvents still struggle to reach, in terms of efficiency, the same performance as those fabricated with halogenated solvents. The reason behind this is the non-optimal nanostructure of the active layer obtained with green solvents. Additives in solution have been used to fine-tune the nanostructure and improve the performance of organic solar cells. Therefore, the identification of non-halogenated additives and the study of their effects on the device performance and stability are of primary importance. In this work, we propose the use of diphenyl ether (DPE) as additive, in combination with the non-halogenated solvent o-xylene, to fabricate organic solar cells with a completely halogen-free process. Thanks to the addition of DPE, a best efficiency of 11.7% have been obtained for the system TPD-3F:IT-4F, an increase over 15% with respect to the efficiency of devices fabricated without additive. Remarkably, the stability under illumination of the solar cells is also improved when DPE is used. The addition of DPE has effects on the molecular organization in the active layer, with an enhancement in the donor polymer ordering, showing a higher domain purity. The resulting structure improves the charge carrier collection, leading to a superior short-circuit current and fill factor. Furthermore, a reduction of the non-radiative recombination losses and an improved exciton diffusion, are the results of the superior molecular ordering. With a comprehensive insight of the effects of DPE when used in combination with a non-halogenated solvent, our study provides an approach to make the fabrication of organic solar cell environmentally friendlier and more suitable for large scale production.

Layered 2D perovskites are making inroads as materials for photovoltaics and light emitting diodes, but the photophysics of their optical excitations is still debated. Although their large exciton binding energies should hinder charge separation, significant evidence has been uncovered for an abundance of free carriers. Several explanations have been proposed, like exciton splitting at grain boundaries or polaron formation, without clarifying yet if excitons form and then split, or if the formation is prevented by competing relaxation processes. Here we address exciton stability in layered PEA2PbI4 in n = 1 Ruddlesden-Popper phase, both in form of thin film and single crystal. Samples are resonantly excited to directly inject cold excitons, whose dissociation is then demonstrated with femtosecond differential transmission. The results presented here establish the intrinsic nature of exciton dissociation in 2D Ruddlesden-Popper layered perovskites, demonstrating that they are free carrier semiconductors like their 3D counterparts, belonging to a universal photophysical framework.

Hybrid lead halides CH3NH3PbX3 (X = I, Br, and Cl) have emerged as a new class of semiconductors for low-cost optoelectronic devices with superior performance. Since their perovskite crystal structure may have lattice instabilities against polar distortions, they are also being considered as potential photo-ferroelectrics. However, so far, research on their ferroelectricity has yielded inconclusive results and the subject is far from being settled. Here, we investigate, using a combined experimental and theoretical approach, the possible presence of electric polarization in tetragonal and orthorhombic CH3NH3PbBr3 (T-MAPB and O-MAPB). We found that T-MAPB does not sustain spontaneous polarization but, under an external electric field, it is projected into a metastable, ionic space-charge electret state. The electret can be frozen on cooling, producing a large and long-lasting polarization in O-MAPB. Molecular dynamics simulations show that the ferroelastic domain boundaries are able to trap charges and segregate ionic point defects, thus playing a favorable role in the stabilization of the electret. At lower temperatures, the lack of ferroelectric behavior is explained using first principles calculations as the result of the tight competition among many metastable states with randomly oriented polarization; this large configurational entropy does not allow a single polar state to dominate at any significant temperature range.

The potential of silicon-based fluorescent platforms for the detection of trace toxic metal ions was investigated in an aqueous environment. To this aim, silicon chips were first functionalized with amino groups, and fluorescein organic dyes, used as sensing molecules, were then covalently linked to the surface via formation of thiourea groups. The obtained hybrid heterostructures exhibited high sensitivity and selectivity towards copper(II), a limit of detection compatible with the recommended upper limits for copper in drinking water, and good reversibility using a standard metal–chelating agent. The fluorophore–analyte interaction mechanism at the basis of the reported fluorescence quenching, as well as the potential of performance improvement, were also studied. The herein presented sensing architecture allows, in principle, tailoring of the selectivity towards other metal ions by proper fluorophore selection, and provides a favorable outlook for integration of fluorescent chemosensors with silicon photonics technology.

The rate of light emission per unit carrier concentration, or radiative rate, is a fundamental semiconductor parameter that determines the limit photoconversion efficiency of solar cells. In hybrid perovskites, a champion materials class for photovoltaics, optical emission results from a bimolecular process, so that the radiative rate depends on the carrier density and cannot be directly measured with standard techniques. Instead, it is estimated either from UV-Vis absorption or from the kinetics of photoexcitation decays in time-resolved spectroscopy experiments. In this work, an ultrafast radiometric experiment is introduced to directly assess the radiative decay rate in perovskite thin films through a calibrated measurement of the instantaneous photoluminescence flux under pulsed laser excitation. The measured radiative decay rate is found to be significantly lower than the second order decay constant determined from photoluminescence decay kinetics, contrary to what is often assumed; it is also 50-100 times slower than estimates for a plasma of free excitons and free charged carriers, obtained from absorption coefficients through optical reciprocity relations. We attribute the microscopic origin of the measured low radiative rate to the formation of a population of dark excitations, specifically large polarons. Our results provide a coherent framework to rationalize radiative and non-radiative carrier recombination processes in metal halide perovskites, as well as the photophysical basis to optimize device performances for this emerging class of semiconductors.

In this work graphene coatings have been deposited on aluminum alloy samples to investigate whether they can improve wear strength and promote friction reduction, which means components reliability...

Manipulation by external pressure of the optical response of 2D Metal Halide Perovskites (MHPs) is a fascinating route to tune their properties and promote the emergence of novel features. We investigate here DA

The gut microbiota is constituted by more than 40,000 bacterial species involved in key processes including high order brain functions. Altered composition of gut microbiota has been implicated in psychiatric disorders and in modulating the efficacy and safety of psychotropic medications. In this work we characterized the composition of the gut microbiota in 38 patients with schizophrenia (SCZ) and 20 healthy controls (HC), and tested if SCZ patients with different response to antipsychotics (18 patients with treatment resistant schizophrenia (TRS), and 20 responders (R)) had specific patterns of gut microbiota composition associated with different response to antipsychotics. Moreover, we also tested if patients treated with typical antipsychotics (n = 20) presented significant differences when compared to patients treated with atypical antipsychotics (n = 31). Our findings showed the presence of distinct composition of gut microbiota in SCZ versus HC, with several bacteria at the different taxonomic levels only present in either one group or the other. Similar findings were observed also depending on treatment response and exposure to diverse classes of antipsychotics. Our results suggest that composition of gut microbiota could constitute a biosignatures of SCZ and TRS.

Graphene is an amazing material that finds application in many fields. In particular, graphene can be used as anti-friction material. Even if graphene has been already tested as lubricants additive, the use as friction reduction coating is not widely investigated. In this paper, the tribological performance of graphene-coated polymers has been investigated. In particular ABS (Acrylonitrile Butadiene Styrene) and PC-ABS (PolyCarbonate-Acrylonitrile Butadiene Styrene) have been investigated as polymers widely used in industrial field. Samples have been coated with graphene by means of a dedicated procedure. Tribological performance has been evaluated by ball on disk tests, taking into consideration different travelled distances in order to evaluate also the coating wear strength. Results show that graphene coat may reduce coefficient of friction of the tested materials although the wear strength of the coating is quite weak.

Friction and wear affect machine reliability, efficiency and safety, increasing the maintenance and operating costs. A reduction of the coefficient of friction (CoF) of sliding parts would increase...

Spline couplings are mechanical components widely used to transmit torque between rotating parts. Although they are well known components, critical issues such as wear damage and un haven loads affect them especially when working in misaligned conditions. Wear damage appears on engaging teeth bringing to component failures. The main way to reduce wear damage is to lubricate the engaging teeth or to apply surface coatings. In this work wear damage on spline coupling was investigated and a compound made of grease added with graphene has been tested against standard lubricants in order to find out if it may improve the wear strength of these components. Experimental tests were performed by means of both standard testing machine provided by a particular testing device and dedicated test rig, designed to perform tests with misaligned spline couplings. Preliminary results show that the presence of graphene improves the grease performance, reducing the coefficient of friction (bringing to a reduction of uneven overloads and wear).

The success of lead halide perovskites as active materials in solar cells and light-emitting diodes (LEDs) is often traced back to the unique properties of their optical excitations. At room temperature and under all device operating conditions, photoexcitation of perovskites creates free carriers and not bound excitons, even in compounds with exciton binding energy several times larger than room temperature thermal energy. As a consequence, absorbed photons can be readily converted in an electric current of electrons and holes to be collected at perovskite edges, leading to efficient solar cells. A thorough review of the large body of experimental evidence on perovskite photophysics however leads to quite a different picture, where excitons are anything but negligible. First of all, they are responsible for the very large absorption coefficients close to the band gap, which can reach as much as 105 cm−1. The magnitude of such an effect depends on the exciton binding energy, whose value proved to be elusive and tricky to assess. Second and more surprising, excitons are responsible for most light emission in perovskites, in spite of being greatly outnumbered by free carriers. The resulting dynamics of optical emission is governed by the ratio between exciton formation through pairing of free carriers and exciton radiative recombination. When the importance of excitons is taken into account, new avenues in lead halide perovskites appear more clearly, particularly the rise of layered, bidimensional (2D) perovskites, where excitonic effects are further enhanced, without compromising the fact that free carriers are the majority of photexcitations.

Hybrid lead halides CH

The surface-initiated Rolling Contact Fatigue (RCF) including pitting and micro-pitting is one of the key issues affecting the reliability of tribological components such as gears and bearings used in various devices. In this work, a surface-initiated crack Finite Element (FE) model which considers the effect of lubricant on crack faces was developed to investigate surface-initiated RCF using an automatic crack propagating Python script. Different lubricating states, initial crack parameters and loading conditions were simulated to analyze the evolution of crack propagation and the Stress Intensity Factors (SIFs). The RCF crack propagation path and life were predicted by employing the Maximum Tangential Stress (MTS) criterion coupled with the Paris’s law. A typical RCF failure is predicted in the numerical simulation. Results reveal that the lubricating pressurization dominates the surface-initiated RCF. In addition, the initial crack angle has a significant effect on the RCF crack propagation path and the fatigue life.

Pin-on-disc method is increasingly used to evaluate the tribological behavior of thin hard coatings. At present, ISO 18535 is the only standard applying to hard coatings tribology and it prescribes that investigations do not extend past the coating failure. This approach followed by many researchers is inadequate though for a complete characterization of a coated system. A novel approach is proposed in this paper, at a preliminary stage, to characterize coated systems thoroughly. Friction curves with a suitable shape are resorted to, so that two representative friction coefficients can be extracted, one before and the other after coating failure. Results with a PVD TiN coating are presented showing that it is possible with this coating to get friction curves with the desired shape in specific testing conditions.

Major depressive disorder (MDD) is a common severe psychiatric illness, exhibiting sub-optimal response to existing pharmacological treatments. Although its etiopathogenesis is still not completely understood, recent findings suggest that an altered composition of the gut microbiota might play a role. Here we aimed to explore potential differences in the composition of the gut microbiota between patients with MDD and healthy controls (HC) and to identify possible signatures of treatment response by analyzing two groups of MDD patients characterized as treatment-resistant (TR) or responders (R) to antidepressants. Stool samples were collected from 34 MDD patients (8 TR, 19 R and 7 untreated) and 20 HC. Microbiota was characterized using the 16S metagenomic approach. A penalized logistic regression analysis algorithm was applied to identify bacterial populations that best discriminate the diagnostic groups. Statistically significant differences were identified for the families of Paenibacillaceae and Flavobacteriaceaea, for the genus Fenollaria, and the species Flintibacter butyricus, Christensenella timonensis, and Eisenbergiella massiliensis among others. The phyla Proteobacteria, Tenericutes and the family Peptostreptococcaceae were more abundant in TR, whereas the phylum Actinobacteria was enriched in R patients. Moreover, a number of bacteria only characterized the microbiota of TR patients, and many others were only detected in R. Our results confirm that dysbiosis is a hallmark of MDD and suggest that microbiota of TR patients significantly differs from responders to antidepressants. This finding further supports the relevance of an altered composition of the gut microbiota in the etiopathogenesis of MDD, suggesting a role in response to antidepressants.

Individuals with severe psychiatric disorders have a reduced life expectancy compared to the general population. At the biological level, patients with these disorders present features that suggest the involvement of accelerated aging, such as increased circulating inflammatory markers and shorter telomere length (TL). To date, the role of the interplay between inflammation and telomere dynamics in the pathophysiology of severe psychiatric disorders has been scarcely investigated. In this study we measured T-lymphocytes TL with quantitative fluorescent in situ hybridization (Q-FISH) and plasma levels of inflammatory markers in a cohort comprised of 40 patients with bipolar disorder (BD), 41 with schizophrenia (SZ), 37 with major depressive disorder (MDD), and 36 non-psychiatric controls (NPC). TL was shorter in SZ and in MDD compared to NPC, while it was longer in BD (model F(6, 137) = 20.128, p = 8.73 × 10(−17), effect of diagnosis, F(3) = 31.870; p = 1.08 × 10(−15)). There was no effect of the different classes of psychotropic medications, while duration of treatment with mood stabilizers was associated with longer TL (Partial correlation controlled for age and BMI: correlation coefficient = 0.451; p = 0.001). Levels of high-sensitivity C-Reactive Protein (hsCRP) were higher in SZ compared to NPC (adjusted p = 0.027), and inversely correlated with TL in the whole sample (r = −0.180; p = 0.042). Compared to NPC, patients with treatment resistant (TR) SZ had shorter TL (p = 0.001), while patients with TR MDD had higher levels of tumor necrosis factor-α (TNFα) compared to NPC (p = 0.028) and to non-TR (p = 0.039). Comorbidity with cardio-metabolic disorders did not influence the observed differences in TL, hsCRP, and TNFα among the diagnostic groups. Our study suggests that patients with severe psychiatric disorders present reduced TL and increased inflammation.

International audience; Nanosheets of two mixed linker (anilate/carboxylate)/YbIII-based two-dimensional (2D) layered coordination polymers (CPs) are herein reported. Bulky sized CPs, formulated as [Yb4(ClCNAn)5(DOBDC)1(DMSO)10]n·(DMSO)2 (1) and [Yb2(ClCNAn)2(F4BDC)(DMSO)6]n (2), are formed by two-dimensional neutral polymeric networks based on YbIII ions, heterosubstituted ClCNAn2– anilate, and dicarboxylate linkers (DOBDC2– in 1; F4BDC2– in 2): in 1, neighbor layers are eclipsed and form six-membered rings showing either hexagonal cavities, formed by ClCNAn2– and YbIII ions or rectangular cavities formed by ClCNAn2–, DOBDC2–, and YbIII while distorted square-like cavities formed by ClCNAn2–, F4BDC2–, and YbIII are obtained in 2. The 1 and 2 nanosheets, that is, 1-NS and 2-NS, are produced by exfoliation of bulk CPs by the well-known top-down approach and characterized by atomic force microscopy and high resolution transmission electron microscopy. The 1-NS and 2-NS show thickness in the range of 1–5 nm, whereas the lateral dimensions are in the micrometer scale and the presence of well-defined lattice fringes, key evidence of their robustness. Remarkably the powder X-ray diffraction (PXRD) patterns highlight that the crystallinity is retained at the nanoscale level. Nanosheets photophysics are investigated by an innovative Multiprobe Approach where lifetime, photoluminescence (PL) and integrated PL are simultaneously measured in order to study how these parameters can be affected by the presence of the different ligands. These advanced photophysical studies pave the way to challenging luminescent sensing applications and to contribute to the ongoing research on fabricating robust and crystalline hybrid (organic/inorganic) lanthanide sheetlike 2D nanomaterials.

This paper proposes a novel method to predict the spur gear pair’s static transmission error based on the accuracy grade, in which manufacturing errors (MEs), assembly errors (AEs), tooth deflections (TDs) and profile modifications (PMs) are considered. For the prediction, a discrete gear model for generating the error tooth profile based on the ISO accuracy grade is presented. Then, the gear model and a tooth deflection model for calculating the tooth compliance on gear meshing are coupled with the transmission error model to make the prediction by checking the interference status between gear and pinion. The prediction method is validated by comparison with the experimental results from the literature, and a set of cases are simulated to study the effects of MEs, AEs, TDs and PMs on the static transmission error. In addition, the time-varying backlash caused by both MEs and AEs, and the contact ratio under load conditions are also investigated. The results show that the novel method can effectively predict the range of the static transmission error under different accuracy grades. The prediction results can provide references for the selection of gear design parameters and the optimization of transmission performance in the design stage of gear systems.

Reference tests are widely used to calibrate scientific instruments but are potential candidate to establish technical diagnosis procedures for scientific instruments too. A reference test is currently lacking in tribology. Though, it would allow users to check that tribometers are properly working and may also form a yardstick for cross-laboratory comparative studies. In this paper two easy-to-use reference testing procedures for the diagnosis of commercial pin-on-disc tribometers are established resorting to a special no-wear test setup in EHL conditions. Several tests were carried out with two tribometers and two commercial oils, and both standardized testing modes were investigated: unidirectional-rotating and linear-reciprocating mode. The friction curves from more than 350 tests were analyzed to generate meaningful statistics supporting the robustness of these procedures. The test setup proved to be suited to the task since the summary of the results showed an excellent repeatability of friction curves concerning appearance and average values.

Optical pump-probe spectroscopy is a crucial tool to investigate the excited state behaviour of materials and is especially useful to investigate the photoexcitation dynamics of bulk heterojunctions as found in organic solar cells. Most common techniques for such investigations involve pulses with an energy density in the range of several tens of J cm(-2), emitted with kHz repetition rate. Such pulse energy can entail non-linear processes due to the formation of high carrier concentrations and can furthermore severely damage the sample material. Here we introduce a softer approach with pulses of nJ cm(-2) energy density and a photon flux which is more than three orders of magnitude lower than in regular techniques. We show the capability of our low-cost and easy to make set-up by investigating two prototypical donor-acceptor polymers, C-PCPDTBT and its silicon variant Si-PCPDTBT. Given the high pulse repetition rate in the MHz regime, we are readily able to monitor sample changes of 10(-5) and find exciton lifetimes of 108 and 150 ps for C- and Si-PCPDTBT respectively.