Quantifying the strength and durability of induced immunity to HIV infection in women engaging in unprotected sexual contacts with infected men

Evidence is accumulating that exposure to human immunodeficiency virus (HIV) can lead to an increased resistance or immunity to subsequent infection. A multirisk model that permits either induced immunity or infection to develop after heterosexual inoculation with HIV is shown to be compatible with a wide spectrum of disparate male-to-female transmission data.When the model is applied to time-dependent, HIV-seroprevalence data, the probability that an unexposed woman would remain unexposed after an unprotected contact with an infected man was estimated to be greater than 0.95 on the average. Thus, it would require at least 14 unprotected sexual contacts with HIV-infected men for 50% of an unexposed cohort of women to become exposed to the virus. This suggests that there is a low probability that HIV virions will be found to have penetrated the mucosal barriers of the reproductive tract after a contact.The model also predicts, that the average woman whose mucosal barriers have been breached by HIV has a significant probability of developing immunity to the virus rather than infection. Modelling data for a cohort of unexposed Nairobi women leads to the prediction that the probability of acquiring induced immunity per contact is about 60% of the probability of acquiring the disease per contact.The modelling results also predict that those who had developed resistance to HIV run the small, but significant risk of becoming infected nonetheless by continuing high-risk behavior. For the common contact rate of ten per month, the modelling predicts that the HIV-transmission risk per contact for unexposed women in the Nairobi cohort is 1/178 while the transmission risk for the cohort's immunized women is 1/1548. These numbers suggest that HIV infection is difficult to transmit through heterosexual intercourse on the average and that male-to-female HIV-transmission risk per contact for African women lies between 1/178 and 1/1548.Direct confirmation of the predictions in the last paragraph has been subsequently observed in two completely independent studies. The Nairobi research team recently reported that a notable number of Nairobi prostitutes previously identified to be members of the HIV-resistant group became infected nonetheless. Second, in a study of 174 sexually monogamous, discordant couples in Rakai, Uganda reporting contacts rates of nine to ten per month, the male-to-female HIV-transmission risk per contact was found to be 1/769 by direct measurement, a value that falls between the above limits of 1/178 and 1/1548 predicted by the modelling. Thus, a second major prediction of this paper has been directly confirmed, and induced immunity to HIV is limited and not absolutely protective.Circumstantial evidence suggests that the induced immunity to HIV predicted by the model could be generated and/or initiated by nonspecific innate immune responses, specific immunological responses, including IgA-mediated mucosal immunity and cytotoxic T lymphocytes (CTL) immunity, or some combination of the above. It is suggested here, that a decrease in the ability of HIV virions to penetrate the protective mucus layer of the reproductive tract may be a prerequisite, cofactor, or the principle cause of the induced immunity or resistance demonstrated to exist in this paper. The value of the probability that induced immunity to HIV will develop after a contact is shown to be a sensitive function of the woman's human leucocyte antigen (HLA) supertype profile.     

Deriving correction functions to model the efficiency of noise barriers with complex shapes using boundary element simulations

The boundary element method (BEM) is a commonly used method to compute the insertion loss of noise barriers having arbitrary cross-sections. For large scale three-dimensional problems, however, the BEM is not feasible. On the other hand, standardized calculation methods for noise mapping are efficient, but shapes other than the straight barrier cannot be properly calculated. Attempts to merge these two approaches by using BEM to derive correction functions based on geometrical quantities such as source and target angle as well as the path length elongation between source and receiver caused by the barrier were usually focused on a small set of barrier types, dimensions, absorptive configurations, source or receiver positions. The main objective of this study is to investigate which functions based on the most common geometrical parameters are well suited for approximating the efficiency of different types of barriers, dimensions and absorptive configurations. To achieve this, numerous combinations of 7 different barrier types, different heights and widths as well as 3 different absorptive configurations were simulated using the 2D BEM for 8 different source positions. The octave-band-wise efficiency, i.e. the frequency-dependent gain in insertion loss compared to an equally high, fully reflective straight barrier was used as a basis for the correction functions. Linear as well as polynomial models were compared yielding a polynomial of third degree in the source and fourth degree in the target angle as the best model. Effects on the error using uniform sampling in the target angle instead of a uniform receiver grid as a basis for the correction functions are also investigated. Furthermore, wide-band efficiencies based on standardized traffic emission spectra are calculated showing small errors compared to single-band errors, in particular in the high-frequency range. A linear interpolation scheme is suggested to deal with barriers having dimensions not simulated in this work.     

Reduction of low‐frequency noise in multilayer MoS2 FETs using a Fermi‐level depinning layer

Two‐dimensional transition metal dichalcogenides (TMDCs) are potential candidate materials for future thin‐film field effect transistors (FETs). However, many aspects of this device must be optimized for practical applications. In addition, low‐frequency noise that limits the design window of electronic devices, in general, must be minimized for TMD‐based FETs. In this study, the low‐frequency noise characteristics of multilayer molybdenum disulphide (MoS₂) FETs were investigated in detail, with two different contact structures: titanium (Ti) metal–MoS₂ channel and Ti metal–TiO₂ interlayer–MoS₂ channel. The results showed that the noise level of the device with a TiO₂ interlayer reduced by one order of magnitude compared with the device without the TiO₂ interlayer. This substantial improvement in the noise characteristics could be explained using the carrier number of fluctuation model. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Effect of temperature–bias annealing on the hysteresis and subthreshold behavior of multilayer MoS2 transistors

The transfer characteristics (I_D–V_G) of multilayers MoS₂ transistors with a SiO₂/Si backgate and Ni source/drain contacts have been measured on as‐prepared devices and after annealing at different temperatures (T_ann from 150 °C to 200 °C) under a positive bias ramp (V_G from 0 V to +20 V). Larger T_ann resulted in a reduced hysteresis of the I_D–V_G curves (from ～11 V in the as‐prepared sample to ～2.5 V after T_ann at 200 °C). The field effect mobility (～30 cm² V^–1 s^–1) remained almost unchanged after the annealing. On the contrary, the subthreshold characteristics changed from the common n‐type behaviour in the as‐prepared device to the appearance of a low current hole inversion branch after annealing. This latter effect indicates a modification of the Ni/MoS₂ contact that can be explained by the formation of a low density of regions with reduced Schottky barrier height (SBH) for holes embedded in a background with low SBH for electrons. Furthermore, a temperature dependent analysis of the subthreshold characteristics revealed a reduction of the interface traps density from ～9 × 10¹¹ eV^–1cm^–2in the as‐prepared device to ～2 × 10¹¹ eV^–1cm^–2after the 200 °C temperature–bias annealing, which is consistent with the observed hysteresis reduction.

Schematic representation of a back‐gated multilayer MoS₂ field effect transistor (left) and transfer characteristics (right) measured at 25 °C on an as‐prepared device and after the temperature–bias annealing at 200 °C under a positive gate bias ramp from 0 V to +20 V.     

Theoretical study of the reaction of vitamin B6 with 1O2

Singlet oxygen is known to cause oxidative stress in cells, leading to severe damage (e.g., lipid peroxidation, membrane degradation, mutagenic alterations to DNA, protein misfunctionality). Recently, pyridoxine has been discovered to be capable of quenching singlet oxygen, however, the mechanism of this reaction remains essentially unknown. In this work, we have investigated four sets of reactions: 1) 1,3-addition to a double bond connected to a hydrogen-carrying group, resulting in the formation of allylic hydroperoxides; 2) [pi2+pi2] 1,2-cycloaddition to an isolated double bond, resulting in the formation of 1,2-peroxides; 3) 1,4-cycloaddition to a system containing at least two conjugated double bonds, resulting in the formation of the so-called 1,4-peroxides; 4) 1,4-addition to phenols and naphthols with the formation of hydroperoxide ketones. Thermodynamically, reaction 4 and the 6(9), 3(8), and 5(8) cases of reaction 1 are the most exergonic ones, with energies ranging from -16 to -18 kcal mol(-1). Furthermore, reaction 4 shows the lowest barrier through the reaction path, and is predicted to be the preferred mechanism for the pyridoxine + singlet-oxygen reaction, which is in agreement with previous experimental results.     

Ab initio studies of push–pull systems

Twelve push–pull ethylene derivatives, NH₂CH=CHX, NH₂C≡CCH=CHX, and ⁻OCHX=CHX (with X=BH₂, C≡N, NO₂, and CH₂ ⁺) have been studied by ab initio calculations. The rotational barrier around the central double bond was chosen as a probe for push–pull effects, as push–pull effects would remove electron density from the central double bond. The amount of reduction of double bond character will increase with the contribution of the zwitterionic resonance hybrid structure. Complete geometry optimizations and calculations of vibrational frequencies were performed for all minima and transition state structures of these 12 systems. The calculations were carried out with the B3LYP and MP2 methods using the 6-311+G(d,p) and the 6-311++G(d,p) basis sets. All the systems investigated exhibited properties consistent with push–pull effects such as elongated C=C double bonds, dipolar electronic structures, and reduced barriers to internal rotation.     

Prospects on integrated electrokinetic systems for decontamination of soil polluted with organic contaminants

Overall, investigations about the utilization of electrokinetic technology alone or in combination with other processes have attracted particular attention in recent years for remediation of soils contaminated with heavy metals and organic compounds. This fact is due to its peculiar benefits together with its capability of operating in a fine and low-permeability matrix. This review aimed to ascertain the most recent developments on the commonly proposed integrated technologies (electrokinetic soil washing, electrokinetics coupled with permeable reactive barriers, electrokinetic-advanced oxidation processes, and bioelectrokinetic remediation), by evaluating the gaps, challenges, and trends of these systems in the last years. Special attention is paid to the current approaches for overcoming the main bottlenecks of electrokinetics concerning scale-up and reduction of electric energy consumption by integration of renewable energies.     

Polyamide nanocomposites

Polyamides are thermoplastic polymers mainly used for producing synthetic fibers. Only about 10% of polyamides are used for plastics production. The market is shared roughly equally between polyamide 6 (polycaprolactam) and polyamide 66 {poly (hexamethyleneadipamide)}. More recently, the research on polyamides led to their nanocomposites. These new hybrid polyamides are reinforced with nanofillers able to increase their main properties and also bring some new interesting characteristics. This paper deals with nanocomposites made of various polyamides and nanofillers; they find application in many engineering fields.