Laser-filament-induced condensation in sub-saturated environments

En ce qui concerne des méthodes d’ensemencement de nuages, les filaments de laser ont des avantages particuliers par rapport à des méthodes traditionnelles. Jusqu’à présent, la condensation induite par le filament de laser a été observée uniquement dans des conditions saturées ou sursaturées. La condensation induite par le filament dans des conditions sous-saturées reste un domaine presqu’inconnu. Nous postulons que la condensation est possible dans des conditions sous-saturées dans la mesure où la cadence des impulsions femtosecondes soit élevé, et qu’une cadence élevée pourrait engendrer une turbulence plus forte, ce qui contribuerait à la condensation. Pour mieux comprendre la condensation dans une condition sous-saturée, nous utilisons une chambre à nuages inversée. Nos recherches permettent d’observer la présence d’agrégats de brume à l’oeil nu ainsi qu’au moyen d’une caméra numérique, et la croissance des gouttelettes d’eau en dessous du filament, ce qui confirme notre hypothèse.Laser filaments have unique advantages compared to other traditional methods when it comes to cloud seeding techniques. Till now, laser filament induced condensation has been observed in saturated or super-saturated conditions alone. Filament induced condensation in sub-saturated conditions remains mostly unexplored. We postulate that condensation is possible in sub-saturated conditions if femtosecond laser pulses of high repetition rate capable of generating a turbulence strong enough to contribute to the condensation process are used. To better understand condensation in sub-saturated conditions, an inverted cloud chamber is used. In our findings, we observe mist packets with and without a digital camera, as well as growth of water droplets under the filament, which in turn confirm our hypothesis

Organic Photodiodes with an Extended Responsivity using Ultrastrong Light-Matter Coupling

In organic photodiodes (OPDs) light is absorbed by excitons, which dissociate to generate photocurrent. Here, we demonstrate a novel type of OPD in which light is absorbed by polaritons, hybrid light-matter states. We demonstrate polariton OPDs operating in the ultra-strong coupling regime at visible and infrared wavelengths. These devices can be engineered to show narrow responsivity with a very weak angle-dependence. More importantly, they can be tuned to operate in a spectral range outside that of the bare exciton absorption. Remarkably, we show that the responsivity of a polariton OPD can be pushed to near infrared wavelengths, where few organic absorbers are available, with external quantum efficiencies exceeding those of a control OPD

Time-resolved imaging of non-diffusive carrier transport in long-lifetime halide perovskite thin films

Owing to their exceptional semiconducting properties, hybrid inorganic-organic perovskites show great promise as photovoltaic absorbers. In these materials, long-range diffusion of charge carriers allows for most of the photogenerated carriers to contribute to the photovoltaic efficiency. Here, time-resolved photoluminescence (PL) microscopy is used to directly probe ambipolar carrier diffusion and recombination kinetics in hybrid perovskites. This technique is applied to thin films of methylammonium lead tri-iodide MAPbI$_3$ obtained with two different fabrication routes, methylammonium lead tribromide (MAPbBr$_3$), and an alloy of formamidinium lead tri-iodide (FAPbI$_3$) and methylammonium lead bromide FA$_{0.85}$MA$_{0.15}$Pb(I$_{0.85}$Br_${0.15}$)$_3$. Average diffusion coefficients in the films leading to the highest device efficiencies and longest lifetimes, i.e., in FA$_{0.85}$MA$_{0.15}$Pb(I$_{0.85}$Br$_{0.15}$)$_3$ and acetonitrile-processed MAPbI$_3$, are found to be several orders of magnitude lower than in the other films. Further examination of the time-dependence shows strong evidence for non-diffusive transport. In particular, acetonitrile-processed MAPbI$_3$ shows distinct diffusion regimes on short and long timescales with an effective diffusion constant varying over 2 orders of magnitude. Our results also highlight the fact that increases in carrier lifetime in this class of materials are not necessarily concomitant with increased diffusion lengths and that the PL quantum efficiency under solar cell operating conditions is a greater indication of material, and ultimately device, quality

A Study of In-Plane Charge Carrier Diffusion and Photon Recycling in Hybrid Organic-Inorganic Perovskites

Plusieurs études récentes prévoient une augmentation de près de 50% de la consommation énergétique mondiale avant 2050. Une chute de la production risque d’avoir des conséquences négatives à la fois sociales et économiques. De plus, les polluants issus des combustibles fossiles, les principales sources d’énergie à l’échelle mondiale, sont à la source de problèmes tels que le réchauffement planétaire, le smog et les pluies acides. Toute réponse à ce défi énergétique doit donc se faire par le moyen d’une alternative propre et renouvelable. En ce sens, l’énergie solaire est un excellent choix. Néanmoins, les panneaux solaires conventionnels restent dispendieux et relativement inefficaces par rapport aux combustibles fossiles. Récemment, la découverte des cellules solaires à base de pérovskites hybrides organique-inorganique a fait l’objet d’un intérêt considérable à travers le monde. Ces dispositifs ont surpassé leurs prédécesseurs organiques à base de colorants parce qu’ils sont plus efficaces, plus simples à fabriquer et moins coûteux. La croissance rapide de l’efficacité des cellules fabriquées à base de ces matériaux, présentement à 25.5%, est inégalée dans l’histoire des cellules solaires. Ceci représente une opportunité unique de créer une nouvelle génération de cellules solaires hautement eÿcaces pouvant stimuler l’industrie solaire. Un panneau solaire est composé de plusieurs cellules photovoltaïques qui sont typiquement reliées en série. Chaque cellule, à son tour, est composée de plusieurs couches; soit une anode, un matériau transporteur d’électrons, un absorbeur, un matériau transporteur de trous et finalement une cathode. Le matériau absorbeur, dans notre cas la pérovskite, sert à la conversion de la lumière entrante en porteurs de charges libres, soit électrons et trous. Le transport des porteurs de charge aux électrodes résulte en une génération d’une différence de potentiel aux bornes de la cellule photovoltaïque. Les pérovskites hybrides, grâce à leur bande interdite (~1.5 eV) approchant la valeur idéale (~1.34 eV) pour l’efficacité de conversion maximale, sont d’excellents absorbeurs. Cependant, il reste beaucoup à découvrir en ce qui concerne la physique fondamentale des porteurs de charges permettant ces valeurs d’efficacité aussi élevées. Plus spécifiquement, comprendre l’influence des processus de recombinaison et de diffusion de porteurs de charges sur les efficacités de conversion énergétique continue à poser un défi à la communauté de recherche en pérovskites. La grande majorité des expériences initiales telles que la photoluminescence résolue en temps (TRPL) ignorent les propriétés latérales du matériau et assument des valeurs idéales pour les conditions de frontières. De plus, les études effectuées jusqu’à présent sur la forme/structure/frontières des grains demeurent inconclusives.----------Abstract Over the next few decades, global energy consumption has been predicted to increase by nearly 50%. The possibility of a shortfall in production or availability could have severe socioeconomic repercussions. In addition, fossil fuels are the primary source of pollutants leading to climate change, smog, acid rain along with various health problems. Hence, any response to this challenge must include a plan to replace fossil fuels with clean and renewable energy sources. Solar energy, which draws upon our nearly infinite supply of solar irradiation, is widely considered to be our most important resource for a sustainable energy future. At present, however, conventional solar panels remain expensive and relatively ineÿcient, when compared to their fossil fuel alternatives. Despite making headlines internationally, hybrid organic-inorganic perovskite (HOIP) solar cells, are a very recent development in solar science. These new devices largely surpass their organic and dye-sensitized predecessors in terms of conversion eÿciency, fabrication simplicity and materials cost. The rapid growth in perovskite solar cell power conversion eÿciencies, which is currently at 25.5% has been unparalleled. Hence, this is a unique opportunity to create a new generation of highly efficient solar cells which could reinvigorate the energy industry. A solar panel is composed of multiple cells which are typically configured in series. Each solar cell is composed of several layers, such as an anode, an electron transporting layer (ETL), an absorber, a hole transporting layer (HTL), and a cathode. The absorber material, i.e. the hybrid perovskite in our case, converts incident irradiation into free charge carriers, i.e. electrons and holes. The transport of charge carriers to their respective electrodes results in power across a load. Hybrid perovskites, thanks to a bandgap (~1.5 eV) approaching the ideal value (~1.34 eV) for maximum power conversion eÿciency, are phenomenal absorbers. How-ever, much remains to be discovered with respect to the underlying carrier physics producing such high efficiencies. Specifically, understanding the influence of recombination kinetics and diffusion on energy conversion effciencies poses a challenge for the perovskite research community. Most of the initial measurements such as time-resolved photoluminescence (TRPL) ignores lateral material properties and assume ideal boundary conditions when fitting coefficients. Also, studies on the e˙ect of grain shape/structure/boundaries on carrier diffusion remain inconclusive. With the recent surge in microscopic/spectroscopic methods for carrier transport characterization, we observe a greater emphasis on the importance of morphological aspects in shaping device performance

Organic Photodiodes with an Extended Responsivity Using Ultrastrong Light–Matter Coupling

In organic photodiodes (OPDs), light is absorbed by excitons that dissociate to generate photocurrent. Here, we demonstrate a novel type of OPD in which light is absorbed by polaritons, hybrid light–matter states. We demonstrate polariton OPDs operating in the ultrastrong coupling regime at visible and infrared wavelengths. These devices can be engineered to show narrow responsivity with a very weak angle-dependence. More importantly, they can be tuned to operate in a spectral range outside that of the bare exciton absorption. Remarkably, we show that the responsivity of a polariton OPD can be pushed to near-infrared wavelengths, where few organic absorbers are available, with external quantum efficiencies exceeding those of our control OPD

Development & standardization of an in-house IgM indirect ELISA for the detection of parvovirus B19 infections

Background & objectives: Parvovirus B19 infections occur worldwide; the infection is acquired early in childhood but could occur later. B19 is reported to cause infection in childhood febrile illnesses, and arthropathies in adults and children and in end-stage renal disease (ESRD) seen in adults. This study was designed to develop an in-house IgM indirect ELISA for serological screening among patients and controls, and to compare ELISA results with those of nested polymerase chain reaction (nPCR) assay. Methods: An in-house IgM indirect ELISA was standardized using peptide sequence of VP1/VP2 region of parvovirus B19. A total of 201 children and adult with febrile illnesses, 216 individuals with non-traumatic arthropathies, 201 cases of chronic anaemia associated with ESRD and 100 healthy controls were tested. Serum was separated from the blood and subsequently used for DNA extraction. The nested polymerase chain reaction (nPCR) for the detection of B19V DNA was performed using primers targeting the overlapping region of VP1/VP2 capsid protein genes. Results: A total of 618 samples were tested for parvovirus B19 by an in-house IgM indirect ELISA. Among these samples, six were positive by in-house ELISA. The inter-rater agreement between ELISA and PCR assays was calculated using kappa coefficient analysis. The value of κ was 0.77 and the strength of agreement was 'good' (P<0.001). Interpretation & conclusions: The in-house IgM indirect ELISA was found to be simple with high sensitivity and specificity when compared with nPCR and could be used as an alternative to expensive commercial kits in resource-poor settings

Detection of parvovirus B19 in selected high-risk patient groups & their phylogenetic & selection analysis

Background & objectives: Human parvovirus B19V (B19V) is known to be associated with erythema infectiosum commonly in children, aplastic crisis, especially in persons with underlying haemolytic disorders, hydrops fetalis in pregnancies and arthritis. This cross-sectional study was aimed to determine the presence of B19V infection in childhood febrile illnesses, association of B19V with arthropathies and in adult patients with end-stage renal disease (ESRD) on dialysis. The genetic diversity among the sequences was also analysed. Methods: A nested polymerase chain reaction (nPCR) assay was used for B19V DNA targeting VP1/VP2 region and used for testing 618 patients and 100 healthy controls. Phylogenetic analysis on nucleotide and amino acid sequences was carried out to compare our sequences with other Indian strains and global strains. Results: Among 618 samples tested, seven (1.13%) were found positive. The phylogenetic analysis revealed that all the seven sequences belonged to genotype 1 and showed low genetic diversity. The clustering pattern of seven sequences was similar both by nucleotide and by predicted amino acid sequences. The fixed effects likelihood analysis showed no positive or negatively selected sites. Interpretation & conclusions: Seven samples (4 from non-traumatic arthropathies, 2 from patients with ESRD and 1 from febrile illness patient) were found positive by nPCR. When our seven sequences were compared with global strains, the closest neighbour was other Indian strains followed by the Tunisian strains

A novel multiplex real-time PCR for the detection of Salmonella Typhi, Salmonella Paratyphi A and Burkholderia pseudomallei in clinical samples

Enteric fever, caused by infection with Salmonella Typhi or Paratyphi A, B, or C (typhoidal Salmonella) and melioidosis are among the most common bacterial causes of acute febrile illness in tropical and subtropical countries. The diseases are widely spread even in developed countries mainly affecting travellers returning from endemic areas. Melioidosis is an increasingly recognized fatal septicemic infection also mimicking tuberculosis. These pathogens are largely underreported due to lack of sensitive and specific diagnostic tools. In this study, an inhouse multiplex real-time PCR assay was developed for the simultaneous detection of Salmonella Typhi, S. Paratyphi A and B. pseudomallei using specific primers. The inhouse developed assay was evaluated on buffy coat and serum samples collected from patients with acute febrile illness at four different centres. The assay had a detection limit of less than 1 genome copy for S. Typhi and S. Paratyphi A and 18 genome copies per 10 µl of PCR input for B. pseudomallei. Among the 1101 samples tested by multiplex real-time PCR, one (0.09%) sample was positive for S. Typhi. One sample was positive for blood culture identified as S. Typhi but negative by real-time PCR. The samples were negative for S. Paratyphi A and B. pseudomallei. The multiplex real-time assay would be highly useful as a diagnostic aid for the syndromic approach and comprehensive diagnosis of enteric fever and melioidosis. The assay could improve the overall diagnostic capability and be a useful tool during outbreak investigations