Influence of nanotube length and density on the plasmonic terahertz response of single-walled carbon nanotubes

We measure the conductivity spectra of thin films comprising bundled single-walled carbon nanotubes (CNTs) of different average lengths in the frequency range 0.3-1000 THz and temperature interval 10-530 K. The observed temperature-induced changes in the terahertz conductivity spectra are shown to depend strongly on the average CNT length, with a conductivity around 1 THz that increases/decreases as the temperature increases for short/long tubes. This behaviour originates from the temperature dependence of the electron scattering rate, which we obtain from Drude fits of the measured conductivity in the range 0.3-2 THz for 10 $\mu$m length CNTs. This increasing scattering rate with temperature results in a subsequent broadening of the observed THz conductivity peak at higher temperatures and a shift to lower frequencies for increasing CNT length. Finally, we show that the change in conductivity with temperature depends not only on tube length, but also varies with tube density. We record the effective conductivities of composite films comprising mixtures of WS$_2$ nanotubes and CNTs vs CNT density for frequencies in the range 0.3-1 THz, finding that the conductivity increases/decreases for low/high density films as the temperature increases. This effect arises due to the density dependence of the effective length of conducting pathways in the composite films, which again leads to a shift and temperature dependent broadening of the THz conductivity peak.Comment: Submitted to Journal of Physics D. Main manuscript: 9 pages, 8 figures. Supplementary material: 5 pages, 6 figure

Analysis of Multiwalled Carbon Nanotubes as Waveguides and Antennas in the Infrared and the Visible Regimes

The propagation of azimuthally symmetric guided waves in multiwalled carbon nanotubes (MWCNTs) was analyzed theoretically in the mid-infrared and the visible regimes. The MWCNTs were modeled as ensembles of concentric, cylindrical, conducting shells. Slightly attenuated guided waves and antenna resonances due to the edge effect exist for not-too-thick MWCNTs in the far- and mid-infrared regimes. Interband transitions hinder the propagation of guided waves and have a deleterious effect on the performance of a finite-length MWCNT as an antenna. Propagation of surface-plasmon waves along an MWCNT with a gold core was also analyzed. In the near-infrared and the visible regimes, the shells behave effectively as lossy dielectrics suppressing surface-plasmon-wave propagation along the gold core.Comment: 13 pages, 8 figure

Effect of platelet-rich fibrin matrix in complex with artificial material Nubiplant on expression of chondrogenic marker genes and morphogenesis of the nucleus pulposus cells of intervertebral discs in rats

The purpose was to study the barrier and biological properties of platelet-rich fibrin matrix (PRFM), an artificial biopolymer Nubiplant, and a mixture of PRFM / Nubiplant by assessing the viability and morphological characteristics of nucleus pulposus (NP) cells in rats, as well as the expression level of chondrogenic marker genes during cell cultivation in the presence of these matrices.Materials and methods. PRFM was obtained from platelet-rich plasma using a SiO2 coagulation activator. A suspension of nucleus pulposus cells was obtained from the caudal spine of rats. Cultivation was carried out in the presence of one of three matrices — PRFM, Nubiplant, or their mixture for 3, 7, and 14 days under standard culture conditions in an EC-160 incubator (Nüve, Turkey). Observation of the living culture was carried out in the area bordering with the matrix within one field of view using an inverted microscope (Nicon TS100, Japan). The expression of chondrogenic marker genes in the cell culture of the NP was determined by the method of PCR with reverse transcription.Results. The study of the viability and morphological characteristics of NP cells during their cultivation for 3, 7, and 14 days in the presence of PRFM, PRFM / Nubiplant, or Nubiplant showed a decrease in the content of living cells in control samples; in cultures with PRFM and PRFM / Nubiplant, the number of living cells significantly exceeded the control values, aggregation of cells was observed in the area bordering with the matrices from the side of the application. None of the experimental samples showed the outflow of cells to the opposite side of the matrix after 14 days of cultivation; thus, PRFM, Nubiplant, and their mixture can perform barrier functions to keep the cell population in a certain location. Expression of the COL II, ACAN, GPC3, ANXA3, PTN, MGP, and VIM genes by the NP cells during cultivation for 3 and 7 days in the presence of PRFM and PRFM / Nubiplant increased as compared to the control samples.Conclusions. The use of PRFM, Nubiplant, or a mixture of PRFM / Nubiplant during the cultivation of NP cells demonstrated the absence of cell outflow to the opposite side of the studied matrices during the study period (14 days). The use of PRFM, Nubiplant, or a mixture of PRFM / Nubiplant promoted the formation of cell colonies with chondrocyte-like morphology in the zone bordering with the matrices and maintained cell viability throughout the study period. PRFM and PRFM / Nubiplant contributed to the maintenance of the expression of chondrogenic genes in the NP cells in the zone bordering the matrices. The results obtained indicate the positive effect of the matrix based on platelet-rich fibrin on the NP cells and its barrier functions, which is promising for the use of PRMF for preventing the formation of cicatricial adhesion

Fundamental optical processes in armchair carbon nanotubes

Single-wall carbon nanotubes provide ideal model one-dimensional (1-D) condensed matter systems in which to address fundamental questions in many-body physics, while, at the same time, they are leading candidates for building blocks in nanoscale optoelectronic circuits. Much attention has been recently paid to their optical properties, arising from 1-D excitons and phonons, which have been revealed via photoluminescence, Raman scattering, and ultrafast optical spectroscopy of semiconducting carbon nanotubes. On the other hand, dynamical properties of metallic nanotubes have been poorly explored, although they are expected to provide a novel setting for the study of electronﾖhole pairs in the presence of degenerate 1-D electrons. In particular, (n,n)-chirality, or armchair, metallic nanotubes are truly gapless with massless carriers, ideally suited for dynamical studies of TomonagaﾖLuttinger liquids. Unfortunately, progress towards such studies has been slowed by the inherent problem of nanotube synthesis whereby both semiconducting and metallic nanotubes are produced. Here, we use post-synthesis separation methods based on density gradient ultracentrifugation and DNA-based ion-exchange chromatography to produce aqueous suspensions strongly enriched in armchair nanotubes. Through resonant Raman spectroscopy of the radial breathing mode phonons, we provide macroscopic and unambiguous evidence that density gradient ultracentrifugation can enrich ensemble samples in armchair nanotubes. Furthermore, using conventional, optical absorption spectroscopy in the nearinfrared and visible range, we show that interband absorption in armchair nanotubes is strongly excitonic. Lastly, by examining the G-band mode in Raman spectra, we determine that observation of the broad, lower frequency (G!) feature is a result of resonance with non-armchair “metallic” nanotubes. These !ndings regarding the fundamental optical absorption and scattering processes in metallic carbon nanotubes lay the foundation for further spectroscopic studies to probe many-body physical phenomena in one dimension

An international effort towards developing standards for best practices in analysis, interpretation and reporting of clinical genome sequencing results in the CLARITY Challenge

There is tremendous potential for genome sequencing to improve clinical diagnosis and care once it becomes routinely accessible, but this will require formalizing research methods into clinical best practices in the areas of sequence data generation, analysis, interpretation and reporting. The CLARITY Challenge was designed to spur convergence in methods for diagnosing genetic disease starting from clinical case history and genome sequencing data. DNA samples were obtained from three families with heritable genetic disorders and genomic sequence data were donated by sequencing platform vendors. The challenge was to analyze and interpret these data with the goals of identifying disease-causing variants and reporting the findings in a clinically useful format. Participating contestant groups were solicited broadly, and an independent panel of judges evaluated their performance. RESULTS: A total of 30 international groups were engaged. The entries reveal a general convergence of practices on most elements of the analysis and interpretation process. However, even given this commonality of approach, only two groups identified the consensus candidate variants in all disease cases, demonstrating a need for consistent fine-tuning of the generally accepted methods. There was greater diversity of the final clinical report content and in the patient consenting process, demonstrating that these areas require additional exploration and standardization. CONCLUSIONS: The CLARITY Challenge provides a comprehensive assessment of current practices for using genome sequencing to diagnose and report genetic diseases. There is remarkable convergence in bioinformatic techniques, but medical interpretation and reporting are areas that require further development by many groups

Estimating cannibalization rates for pioneering innovations

To evaluate the success of a new product, managers need to determine how much of its new demand is due to cannibalizing the firm’s other products, rather than drawing from competition or generating primary demand. We introduce a time-varying vector error-correction model to decompose the base sales of a new product into its constituent sources. The model allows managers to estimate cannibalization effects and calculate the new product’s net demand, which may be considerably less than its total demand. We apply our methodology to the introduction of the Lexus RX300 using detailed car transaction data. This case is especially interesting because the Lexus RX300 was the first crossover sport utility vehicle (SUV), implying that its demand could come from both the luxury SUV and the luxury sedan categories. Because Lexus was active in both categories, there was a double cannibalization potential. We show how the contribution of the different demand sources varies over time and discuss the managerial implications for both the focal brand and its competitors

Дегенерація міжхребцевих дисків та методи її біологічної корекції

Human physical possibilities limitation caused by intervertebral discs degenerative diseases is a serious medical and social problem in our time. Main signs of intervertebral discs degenerative diseases — cells death, proteoglycane and collagen synthesis decrease. Intervertebral discs degeneration is frequent cause of painful syndrome forming. Today therapy is directed not only on painful syndrome elimination but also on dick’s functions renewing. Modern technologies are frequently based on biological materials using. Injections of proteins activators, biomaterials, different cell types or cell complexes and extracellular matrix, genetically modified cells, and in vitro constructed tissue are used for intravertebral disc regeneration activation. Using one or another therapeutic tactic sufficiently depends on degenerative state expressivity, taking into account the procedure safety.Ограничение физических возможностей человека вследствие дегенеративной болезни межпозвонкового диска является важной медицинской и социальной проблемой современности. Основные признаки дегенеративной болезни межпозвонкового диска — гибель клеток, уменьшение синтеза протеогликана и коллагена. Дегенерация межпозвонкового диска является частой причиной формирования болевого синдрома. В настоящее время терапия направлена не только на устранение болевого синдрома, но и на восстановление функций межпозвонкового диска. Современные технологии часто основаны на использовании биологических материалов. Для активации регенерации межпозвонкового диска используют инъекции белков активаторов, биоматериалов, различных типов клеток или комплексов клеток и экстраклеточного матрикса, генетически модифицированные клетки, in vitro сконструированную ткань. Использование той или иной лечебной тактики в значительной степени зависит от выраженности дегенерации с учетом безопасности процедуры.Обмеження фізичних можливостей людини внаслідок дегенеративної хвороби міжхребцевого диска є важливою медичною й соціальною проблемою нашого часу. Основні ознаки дегенеративної хвороби міжхребцевого диска — загибель клітин, зменшення синтезу протеоглікану та колагену. Дегенерація міжхребцевого диска є частою причиною формування больового синдрому. В наш час терапія спрямована не тільки на усунення больового синдрому, а й на відновлення функцій міжхребцевого диска. Сучасні технології часто основані на використанні біологічних матеріалів. Для активації регенерації міжхребцевого диска використовують ін’єкції білків активаторів, біоматеріалів, різних типів клітин або різних комплексів клітин та різних типів позаклітинного матриксу, генетично модифіковані клітини, in vitro сконструйовану тканину. Вибір тієї або іншої тактики лікування значною мірою визначається ступенем вираженості дегенерації та умовами безпеки проведення процедури