Author Correction: Titanium-carbide MXenes for work function and interface engineering in perovskite solar cells.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Titanium-carbide MXenes for work function and interface engineering in perovskite solar cells.

To improve the efficiency of perovskite solar cells, careful device design and tailored interface engineering are needed to enhance optoelectronic properties and the charge extraction process at the selective electrodes. Here, we use two-dimensional transition metal carbides (MXene Ti3C2Tx) with various termination groups (Tx) to tune the work function (WF) of the perovskite absorber and the TiO2 electron transport layer (ETL), and to engineer the perovskite/ETL interface. Ultraviolet photoemission spectroscopy measurements and density functional theory calculations show that the addition of Ti3C2Tx to halide perovskite and TiO2 layers permits the tuning of the materials' WFs without affecting other electronic properties. Moreover, the dipole induced by the Ti3C2Tx at the perovskite/ETL interface can be used to change the band alignment between these layers. The combined action of WF tuning and interface engineering can lead to substantial performance improvements in MXene-modified perovskite solar cells, as shown by the 26% increase of power conversion efficiency and hysteresis reduction with respect to reference cells without MXene.

Graphene-Induced Improvements of Perovskite Solar Cell Stability: Effects on Hot-Carriers.

Hot-carriers, that is, charge carriers with an effective temperature higher than that of the lattice, may contribute to the high power conversion efficiency (PCE) shown by perovskite-based solar cells (PSCs), which are now competitive with silicon solar cells. Hot-carriers lose their excess energy in very short times, typically in a few picoseconds after excitation. For this reason, the carrier dynamics occurring on this time scale are extremely important in determining the participation of hot-carriers in the photovoltaic process. However, the stability of PSCs over time still remains an issue that calls for a solution. In this work, we demonstrate that the insertion of graphene flakes into the mesoscopic TiO2 scaffold leads to stable values of carrier temperature. In PSCs aged over 1 week, we indeed observe that in the graphene-free perovskite cells the carrier temperature decreases by about 500 K from 1800 to 1300 K, while the graphene-containing cell shows a reduction of less than 200 K after the same aging time delay. The stability of the carrier temperature reflects the stability of the perovskite nanocrystals embedded in the mesoporous graphene-TiO2 layer. Our results, based on femtosecond transient absorption measurements, show that the insertion of graphene can be beneficial for the design of stable PSCs with the aim of exploiting the hot-carrier contribution to the PCE of the PSCs.

Nucleosome loss facilitates the chemotactic response of macrophages.

BACKGROUND: High mobility group box 1 (HMGB1) is a small nuclear protein with two functions. In the nucleus, it helps to wrap DNA around nucleosomes. When secreted, it recruits inflammatory cells and induces cytokine production. Before HMGB1 is secreted from inflammatory cells, it relocates to the cytoplasm, which partially or totally depletes cell nuclei of HMGB1. We previously showed that cells lacking HMGB1 contain 20% fewer nucleosomes and 30% more RNA transcripts levels genome-wide. OBJECTIVE: We hypothesized that the depletion of nuclear HMGB1 plays a role in inflammation that can enhance or complement the role of extracellular HMGB1. METHODS: We analysed the transcriptional profile of wild-type and Hmgb1-/- mouse embryonic fibroblasts (MEFs) as a proxy for cells that have lost HMGB1 from their nuclei. We explored the transcriptome of wild-type and Hmgb1-/- macrophages differentiated in the presence of granulocyte-macrophage colony-stimulating factor, before and after exposure to LPS/IFN-γ. In the same cells, histones and nuclear HMGB1 were quantified. RESULTS: We found that Hmgb1-/- MEFs show a transcriptional profile associated with stress and inflammation responses. Moreover, wild-type macrophages that have secreted HMGB1 because of LPS/IFN-γ exposure rapidly reduce their histone content as much as cells that genetically lack HMGB1. Importantly, unstimulated Hmgb1-/- macrophages activate transcriptional pathways associated with cell migration and chemotaxis. CONCLUSIONS: We suggest that nucleosome loss is an early event that facilitates transcriptional responses of macrophages to inflammation, particularly chemotaxis. HMGB1's dual roles in the nucleus and in the extracellular space appear to be complementary.

Hepatitis B virus blood screening: impact of nucleic amplification technology testing implementation on identifying hepatitis B surface antigen non-reactive window period and chronic infections.

BACKGROUND: Despite improvements in hepatitis B surface antigen (HBsAg) test sensitivity, post-transfusion hepatitis B virus (HBV) infection still occurs because HBsAg is undetectable during the early window phase (WP) of the infection, in the convalescence core window phase of the infection, or in serologically silent chronic hepatitis or in mutant forms of HBV. HBV-DNA screening using high sensitivity nucleic amplification technology (NAT) assays has recently been introduced to reduce the residual risk of transmission of HBV by transfusion of blood components. MATERIALS: Over 1 year 75 063 donations were individually screened for HBV-DNA by the Ultrio Procleix assay on the Tigris platform. The donations were collected in the Latium region, an area of the central Italy, and they accounted for the 40% of the total blood units collected in this area per year. The initial reactive samples were re-tested and confirmed by the discriminatory HBV assay. Additional HBV serological markers were also performed. Suspected WP infections were followed-up to monitor the development of the immune response. All HBV-DNA-positive donors were called back to check up their infectious status. RESULTS: The results of testing the 75 063 donations are: 33 donations HBsAg positive, 31 out of them HBV-DNA-positive and two HBV-DNA negative; 22 donations HBsAg-negative but HBV-DNA positive with low viral load. Six of the 22 were found to be consistently HBV-DNA reactive whereas the remaining 16 donations showed inconsistent results on multiple NAT retesting. One WP infection was confirmed by the follow-up of the donor for 3 months following the index blood donation. CONCLUSIONS: In the donor population of the Latium region, NAT screening has revealed a higher than expected number of donors who were HBsAg non-reactive but HBV-DNA-positive with three donors showing HBV-DNA as the only marker of infection. The adoption of genome screening has increased the safety of the blood supply and has also contributed to the protection of donor health by identifying either WP or clinically silent infections.

In situ hybridization analysis of interstitial C-heterochromatin in marker chromosomes of two human melanomas.

Two distinct marker chromosomes, presenting with intercalated C- and distamycin A-Dapi-positive regions, were observed in a metastatic and a primary melanoma. To establish the origin of these heterochromatic sequences, we performed in situ hybridization analysis using specific probes for human repetitive DNA. The marker of the primary melanoma, m2, a der 16 chromosome resulting from the translocation of the 1q12-qter segment to band q23 of chromosome 16, showed specific hybridization with Sau3A but not with EcoRI sequences at the interstitial C-band. Thus the origin of this region from the normal chromosome 1 pericentromeric heterochromatin, containing both EcoRI and Sau3A sequences, could be established. On the other hand, the marker of the metastatic melanoma, m1, a der 1 chromosome showing an abnormally banded region inserted between 1q11 and 1q21-qter, failed to give any hybridization signals at the C- and distamycin A-Dapi-positive band when the same EcoRI and Sau3A probes were used. Furthermore, no hybridization was observed using either a probe for SatIII-specific sequences (QP23), mapping to chromosome 9 heterochromatic block, or LS6BB, a ribosomal DNA probe. From these data we speculate that more complex molecular rearrangements may have occurred during the transposition of heterochromatin from its original site to m1. The heterochromatin change found in m1 may be related to advanced stages of malignancy.

Replication pattern of human repeated DNA sequences.

Either aphidicolin- or thymidine-synchronized human HL-60 cells were used to study the replication pattern of a family of human repetitive DNA sequences, the Eco RI 340 bp family (alpha RI-DNA), and of the ladders of fragments generated in total human DNA after digestion with XbaI and HaeIII (alpha satellite sequences). DNAs replicated in early, middle-early, middle-late and late S periods were labelled with BUdR or with [3H]thymidine. The efficiency of the cell synchronization procedure was confirmed by the transition from a high-GC to a high-AT average base composition of the DNA synthesized going from early to late S periods. By hybridizing EcoRI 340 bp repetitive fragments to BUdR-DNAs it was found that this family of sequences is replicated throughout the entire S period. Comparing fluorograph densitometric scans of [3H]DNAs to the scans of ethidium bromide patterns of total HL-60 DNA digested with XbaI and HaeIII, it was observed that DNA synthesized in different S periods is characterized by approximately the same ladder of fragments, while the intensity of each band may vary through the S phase; in particular, the XbaI 2.4 kb fragment becomes undetectable in late S.

Linkage in human heterochromatin between highly divergent Sau3A repeats and a new family of repeated DNA sequences (HaeIII family).

The hybridization of human DNA with three non-cross-hybridizing monomers (68 bp in length) of the heterochromatic Sau3A family of DNA repeats, indicates the coexistence within a Sau3A-positive genomic block of divergent Sau3A units as well as of unrelated sequences. To gain some insight into the structure of these human heterochromatic DNA regions, three previously cloned Sau3A-positive genomic fragments (with a total length of approximately 1900 base-pairs (bp] were sequenced. The analysis of the sequences showed the presence of clustered Sau3A units with different degrees of divergence and of two DNA regions of approximately 100 bp and 291 bp in length, unrelated to the family of repeats. A consensus sequence derived from the 24 identified Sau3A monomers presents, among highly variable regions, two less variant regions of 8 bp and 10 bp in length, respectively. The Sau3A-unrelated DNA fragment 291 bp in length, used as a probe on genomic DNA digested with a series of restriction enzymes, defines a "new" family of DNA repeats possessing periodicities for HaeIII (HaeIII family). Sau3A and HaeIII repeats display a high degree of linkage in a collection of Sau3A-positive genomic recombinant phages.

Identification of a human clustered G + C-rich DNA family of repeats (Sau3A family).

Sau3A digestion of human G + C-rich DNA molecules yields discrete bands of approximately 70 and 140 base-pairs, under-represented in A + T-rich DNA molecules and in total DNA. We have cloned the 70 base-pair band in a plasmid vector and isolated a representative recombinant clone that identifies a new human family of repeats, the Sau3A family. The new family has been characterized for a number of parameters: genomic organization; reiteration frequency; sequence analysis; and distribution in a human genomic library. The Sau3A sequence (68 base-pairs in length, 53% G + C) is present in approximately 4 X 10(4) copies/haploid genome; the family is characterized by a cluster organization and is confined to a limited fraction (0.5%) of phages of a human genomic library. Southern blot hybridizations of the cloned sequence to restriction digests of total human DNA and of isolated genomic clones does not show the involvement of Sau3A blocks in long-range periodicities for any of the enzymes tested. The data suggest either a high sequence variability in the family or a complex organization of Sau3A sequence domains.

Molecular organization and chromosomal location of human GC-rich heterochromatic blocks.

From the sequencing of three genomic DNA fragments and PCR amplification products from total human DNA, we have derived the sequence of a 545-bp Sau3A fragment (68% GC), representative of a family of human DNA repeats. Since previous studies suggested its linkage with unrelated Sau3A repeats of 68 bp (54% GC) (beta-satellite sequences), this feature was further investigated by in situ hybridization experiments and by Southern blot analysis of a panel of DNAs from human-Chinese hamster somatic cell hybrids. Both DNA repeats are preferentially localized on the heterochromatic regions of acrocentric chromosomes, on the pericentromeric heterochromatin of chromosome 1, 3 and 9, and on the proximal euchromatic region of the chromosome Y q arm. On chromosome 9, both repeats are part of a 2.7-kb higher-order repeat unit. These results and the Southern blot analysis on partial digests of total DNA, suggest that the linkage between the two repetitive DNA sequences is a constant feature throughout the genome. Furthermore, Southern blot analysis of HpaII-digested and MspI-digested DNA from different human tissues and tumor cell lines indicates that the investigated heterochromatic blocks appear to be subjected to changes in their methylation pattern.

Tutorial on modeling ordered categorical response data.

In the past decade there has been great progress in the development of methodology for analyzing ordered categorical data. Logit and log linear model-building techniques for nominal data have been generalized for use with ordinal data. There are many advantages to using these procedures instead of the Pearson chi-square test of independence to analyze ordered categorical data. These advantages include (a) more complete description of the nature of associations and (b) greater power for detecting population associations. This article introduces logit models for categorical data and shows two ways of adapting them to model ordered categorical data. The models are used to analyze a cross-classification table relating mental impairment and parents' socioeconomic status.

Dealing with discreteness: making 'exact' confidence intervals for proportions, differences of proportions, and odds ratios more exact.

'Exact' methods for categorical data are exact in terms of using probability distributions that do not depend on unknown parameters. However, they are conservative inferentially. The actual error probabilities for tests and confidence intervals are bounded above by the nominal level. This article examines the conservatism for interval estimation and describes ways of reducing it. We illustrate for confidence intervals for several basic parameters, including the binomial parameter, the difference between two binomial parameters for independent samples, and the odds ratio and relative risk. Less conservative behavior results from devices such as (1) inverting tests using statistics that are 'less discrete', (2) inverting a single two-sided test rather than two separate one-sided tests each having size at least half the nominal level, (3) using unconditional rather than conditional methods (where appropriate) and (4) inverting tests using alternative p-values. The article concludes with recommendations for selecting an interval in three situations-when one needs to guarantee a lower bound on a coverage probability, when it is sufficient to have actual coverage probability near the nominal level, and when teaching in a classroom or consulting environment.

Modelling patterns of agreement and disagreement.

This article presents a survey of ways of statistically modelling patterns of observer agreement and disagreement. Main emphasis is placed on modelling inter-observer agreement for categorical responses, both for nominal and ordinal response scales. Models discussed include (1) simple cell-probability models based on Cohen's kappa that focus on beyond-chance agreement, (2) loglinear models for square tables, such as quasi-independence and quasi-symmetry models, (3) latent class models that express the joint distribution between ratings as a mixture of clusters for homogeneous subjects, each cluster having the same 'true' rating, and 4) Rasch models, which decompose subject-by-observer rating distributions using observer and subject main effects. Models can address two distinct components of agreement--strength of association between ratings, and similarity of marginal distributions of the ratings.

Josephson junction coupled to a transmission line: a comparison of different approaches.

The case of a Josephson junction loaded by a transmission line is reexamined, according to the Green's function method, in order to compare the results with those that we previously obtained, analytically and numerically, following a different procedure.

Simple stochastic model for optical tunneling.

A simple model, derived from a Brownian-motion scheme, is capable of interpreting the results of delay-time measurements relative to frustrated total reflection experiments at the microwave scale but also in the visible region. In this framework we also obtain a plausible description of the trajectories (rays) inside the tunneling region, the air gap between two paraffin prisms.

Anomalous pulse delay in microwave propagation: A stochastic process interpretation.

An experiment involving microwave propagation in the near-field region with two horn antennas demonstrated a superluminal behavior which is strongly dependent on the frequency. The models previously proposed are found to be inadequate for interpreting the results. An attempt is made within the framework of a stochastic model, which can be improved by a path-integral analysis.

Anomalous delay in wave propagation and tunneling: a transition-elements analysis of the traversal time.

An alternative model for near-field propagation and optical tunneling is proposed following the lines of the path-integral method developed by Feynman, and in particular by using a transition-elements analysis. Such a model was able to account for the frequency dependency of delay-time results of an experiment involving microwave propagation in the near field using two horn antennas [A. Ranfagni et al., Phys. Rev. E 66, 036111 (2002)]. Furthermore, this approach is also capable of interpreting delay-time results as a function of the barrier width in a frustrated total internal reflection experiment performed at the microwave scale and in the optical region.

Experimental evidence of tunneling as a stochastic process.

A model for tunneling based on stochastic processes proves to be capable of interpreting the results of two experiments at the microwave scale. The first of these consisted of measuring the penetration time in a subcutoff waveguide; the second one, in measuring the shift of a beam in a frustrated total reflection. Said shift which is a measurement of the traversal time of the barrier. In both cases, a peak in the real-time component was evidenced, as predicted by the theoretical model.

Different approach for evaluating dissipation in macroscopic quantum tunneling.

The problem of evaluating dissipative effects in macroscopic quantum tunneling is re-examined for the case of Josephson junctions, with the adoption of an alternative way with respect to several previously proposed and, in some cases, contradictory approaches. The system, which consists of a junction coupled to a transmission line, is analyzed both analytically and numerically. A test of the theoretical model, as compared to the experimental results available, is performed in accordance with a criterion based on a shortening of the traversal time.

Tunneling as a stochastic process: a path-integral model for microwave experiments.

Delay time results obtained in microwave experiments at frequencies above and below the cutoff frequency of different waveguide sections are interpreted on the basis of wave propagation in the presence of dissipative effects. Kac's original suggestion was the starting point for the formulation of a stochastic model, which has now been substantially improved, also in relation to the transition-elements theory of Feynman-Hibbs. In this way, an approach to the problem is provided, which is completely distinct from the ones formulated elsewhere.