Fabrication Of All-inorganic Nanocrystal Solids Through Matrix Encapsulation Of Nanocrystal Arrays

A general strategy for low-temperature processing of colloidal nanocrystals into all-inorganic films is reported. The present methodology goes beyond the traditional ligand-interlinking scheme and relies on encapsulation of morphologically defined nanocrystal arrays into a matrix of a wide-band gap semiconductor, which preserves optoelectronic properties of individual nanoparticles while rendering the nanocrystal film photoconductive. Fabricated solids exhibit excellent thermal stability, which is attributed to the heteroepitaxial structure of nanocrystal matrix interfaces, and show compelling light-harvesting performance in prototype solar cells

Experimental demonstration of superdirective spherical dielectric antenna

An experimental demonstration of directivities exceeding the fundamental Kildal limit, a phenomenon called superdirectivity, is provided for spherical high-index dielectric antennas with an electric dipole excitation. A directivity factor of about 10 with a total efficiency of more than 80\% for an antenna having a size of a third of the wavelength was measured. High directivities are shown to be associated with constructive interference of particular electric and magnetic modes of an open spherical resonator. Both analytic solution for a point dipole and a full-wave rigorous simulation for a realistic dipole antenna were employed for optimization and analysis, yielding an excellent agreement between experimentally measured and numerically predicted directivities. The use of high-index low-loss ceramics can significantly reduce the physical size of such antennas while maintaining their overall high radiation efficiency. Such antennas can be attractive for various high-frequency applications, such as antennas for the Internet of things, smart city systems, 5G network systems, and others. The demonstrated concept can be scaled in frequency

Improving The Catalytic Activity Of Semiconductor Nanocrystals Through Selective Domain Etching

Colloidal chemistry offers an assortment of synthetic tools for tuning the shape of semiconductor nanocrystals. While many nanocrystal architectures can be obtained directly via colloidal growth, other nanoparticle morphologies require alternative processing strategies. Here, we show that chemical etching of colloidal nanoparticles can facilitate the realization of nanocrystal shapes that are topologically inaccessible by hot-injection techniques alone. The present methodology is demonstrated by synthesizing a two-component CdSe/CdS nanoparticle dimer, constructed in a way that both CdSe and CdS semiconductor domains are exposed to the external environment. This structural morphology is highly desirable for catalytic applications as it enables both reductive and oxidative reactions to occur simultaneously on dissimilar nanoparticle surfaces. Hydrogen production tests confirmed the improved catalytic activity of CdSe/CdS dimers, which was enhanced 3-4 times upon etching treatment. We expect that the demonstrated application of etching to shaping of colloidal heteronanocrystals can become a common methodology in the synthesis of charge-separating nanocrystals, leading to advanced nanoparticles architectures for applications in areas of photocatalysis, photovoltaics, and light detection

Suppressed Carrier Scattering In Cds-encapsulated Pbs Nanocrystal Films

One of the key challenges facing the realization of functional nanocrystal devices concerns the development of techniques for depositing colloidal nanocrystals into electrically coupled nanoparticle solids. This work compares several alternative strategies for the assembly of such films using an all-optical approach to the characterization of electron transport phenomena. By measuring excited carrier lifetimes in either ligand-linked or matrix-encapsulated PbS nanocrystal films containing a tunable fraction of insulating ZnS domains, we uniquely distinguish the dynamics of charge scattering on defects from other processes of exciton dissociation. The measured times are subsequently used to estimate the diffusion length and the carrier mobility for each film type within the hopping transport regime. It is demonstrated that nanocrystal films encapsulated into semiconductor matrices exhibit a lower probability of charge scattering than that of nanocrystal solids cross-linked with either 3-mercaptopropionic acid or 1,2-ethanedithiol molecular linkers. The suppression of carrier scattering in matrix-encapsulated nanocrystal films is attributed to a relatively low density of surface defects at nanocrystal/matrix interfaces

HIV and hepatitis C virus infections among hanka injection drug users in central Ukraine: a cross-sectional survey

<p>Abstract</p> <p>Background</p> <p>Ukraine has experienced an increase in injection drug use since the 1990s. An increase in HIV and hepatitis C virus infections has followed, but not measures of prevalence and risk factors. The purposes of this study are to estimate the prevalence of HIV, HCV, and co-infection among injection drug users (IDUs) in central Ukraine and to describe risk factors for HIV and HCV.</p> <p>Methods</p> <p>A sample of 315 IDUs was recruited using snowball sampling for a structured risk interview and HIV/HCV testing (81.9% male, 42% single, average age 28.9 years [range = 18 to 55]).</p> <p>Results</p> <p>HIV and HCV antibodies were detected in 14.0% and 73.0%, respectively, and 12.1% were seropositive for both infections. The most commonly used drug was hanka, home-made from poppy straw and often mixed with other substances including dimedrol, diazepines, and hypnotics. The average period of injecting was 8.5 years; 62.5% reported past-year sharing needles or injection equipment, and 8.0% shared with a known HIV-positive person. More than half (51.1%) reported multiple sexual partners, 12.9% buying or selling sex, and 10.5% exchanging sex and drugs in the past year. Those who shared with HIV positive partners were 3.4 times more likely to be HIV positive than those who did not. Those who front- or back-loaded were 4 times more likely to be HCV positive than those who did not.</p> <p>Conclusion</p> <p>Harm reduction, addiction treatment and HIV prevention programs should address risk factors to stop further spread of both HIV and HCV among IDUs and to the general population in central Ukraine.</p

ОРТОПЕДИЧЕСКОЕ ЛЕЧЕНИЕ БОЛЬНЫХ С ЭНДОДОНТО-ПАРОДОНТАЛЬНЫМ СИНДРОМОМ

In a study in 112 patients with endoparodontal syndrome depending on the availability of orthopedic rehabilitation cal (selective grinding and temporary splinting of teeth) studied the clinical efficacy of the treatment. Increase the periodontal attachment during the 18 months of observation of follow-up was more than you-expression when incorporated into the complex treatment of temporary splinting of teeth. Patients with endoparodontal syndrome with an average severity of periodontal destruction in the presence of the temporary splinting of teeth-coe coefficient of efficiency of treatment was 60% higher, and in severe periodontal lesions – 35% higher. Аs a result of the total evaluation of the dynamics of mobility of the teeth, the depth of periodontal pockets, the value of the periodontal attachment, destruction of the alveolar bone, and microvascular reactivity level of the microcirculatory ensure periodontal tissue formed the rationale for the recommendations of the interim shihning teeth in order to increase the effectiveness of treatment of patients with endoparodontal syndrome.В исследовании у 112 больных с эндопародонтальным синдромом в зависимости от наличия ортопедической реабилитации (избирательное пришлифовывание и временное шинирование зубов) изучена клиническая эффективность лечения. Прирост зубодесневого прикрепления в течение 18 месяцев наблюдения был более выражен при включении в комплекс лечения временного шинирования зубов. У больных с эндопародонтальным синдромом со средней тяжестью поражения пародонта при наличии временного шинирования зубов коэффициент эффективности лечения был на 60% выше, а при тяжелом поражении пародонта – на 35% выше. По результатам суммарной оценки динамики подвижности зубов, глубины пародонтальных карманов, величины зубодесневого прикрепления, деструкции альвеолярной кости, реактивности микрососудов и уровня микроциркуляторного обеспечения тканей пародонта сформировано обоснование для рекомендации временного шинирования зубов с целью повышения эффективности лечения больных с эндопародонтальным синдромом

Photocatalytic Activity Of Core/shell Semiconductor Nanocrystals Featuring Spatial Separation Of Charges

The present study investigates the photocatalytic activity of ZnSe/CdS core/shell semiconductor nanocrystals. These nanoparticles exhibit a spatial separation of photoinduced charges between the core and the shell domains, which makes them potentially viable for photocatalytic applications. Unfortunately, one of the excited charges remains inside the core semiconductor and thus cannot efficiently react with the external environment. Here, we explore this issue by investigating the mechanisms of hole extraction from the ZnSe core to the surface of the CdS shell. In particular, the effect of shell thickness in ZnSe/CdS core/shell nanocrystals on the ability of core-localized charges to perform oxidative reactions was determined. By using a combination of time-resolved spectroscopy and electrochemical techniques, we demonstrate that the use of hole-scavenging surfactants facilitates an efficient transfer of core-localized holes to the surface even in the case of shells exceeding 7 nm in thickness. These measurements further demonstrate that photoinduced holes can be extracted from the core faster than they recombine with shell-localized electrons, indicating that most of the absorbed energy in ZnSe/CdS nanocrystals can be used to drive catalytic reactions

The Effect Of The Charge-separating Interface On Exciton Dynamics In Photocatalytic Colloidal Heteronanocrystals

Ultrafast transient absorption spectroscopy was used to investigate the nature of photoinduced charge transfer processes taking place in ZnSe/CdS/Pt colloidal heteronanocrystals. These nanoparticles consist of a dot-in-a-rod semiconductor domain (ZnSe/CdS) coupled to a Pt tip. Together the three components are designed to dissociate an electron-hole pair by pinning the hole in the ZnSe domain while allowing the electron to transfer into the Pt tip. Separated charges can then induce a catalytic reaction, such as the light-driven hydrogen production. Present measurements demonstrate that the internal electron-hole separation is fast and results in the localization of both charges in nonadjacent parts of the nanoparticle. In particular, we show that photoinduced holes become confined within the ZnSe domain in less than 2 ps, while electrons take approximately 15 ps to transition into a Pt tip. More importantly, we demonstrate that the presence of the ZnSe dot within the CdS nanorods plays a key role both in enabling photoinduced separation of charges and in suppressing their backward recombination. The implications of the observed exciton dynamics to photocatalytic function of ZnSe/CdS/Pt heteronanocrystals are discussed