Testing the validity of THz reflection spectra by dispersion relations

Complex response function obtained in reflection spectroscopy at terahertz range is examined with algorithms based on dispersion relations for integer powers of complex reflection coefficient, which emerge as a powerful and yet uncommon tools in examining the consistency of the spectroscopic data. It is shown that these algorithms can be used in particular for checking the success of correction of the spectra by the methods of Vartiainen et al [1] and Lucarini et al [2] to remove the negative misplacement error in the terahertz time-domain spectroscopy.Comment: 17 pages, 4 figure

Analysis of strength and vibration characteristics of the first working blades of an axial compressor with rotor groove

В данной работе представлен сравнительный анализ результатов модального и структурного расчетов единичной лопатки первой ступени осевого компрессора и лопатки в сборке с пазом. Произведена верификация частот собственных колебаний. Выявлены зоны локализации интенсивностей напряжений при нагружении центробежными силами для различных конструктивных исполнений лопаточного аппарата турбокомпрессора. Показаны возможности снижения напряжений путем выбора наиболее удачной конструкции.This paper presents a comparative analysis of the results of the modal and structural calculations individual blade of the first stage axial compressor and blade assembly to the groove. Verification of the natural frequencies was produced. Identified areas of localization of the intensities of stresses when loaded by centrifugal forces for various design versions of the blade apparatus of the turbocharger. Shown the possibility of reducing stress by selecting the most successful design

Optical gap in herringbone and pi-stacked crystals of 1]benzothieno3,2-b]benzothiophene and its brominated derivative

The optical gap of the organic semiconductor 1]benzothieno3,2-b]benzothiophene and its 2,7-dibrominated analogue is measured in solution and in the crystalline state by means of UV-vis and emission spectroscopy. Bromination leads to a change in molecular packing from herringbone to pi-stacked, resulting in a marked shift in the absorption and emission spectra which is found to be in accordance with TDDFT calculations

The Stacking Faulted Nature of the Narrow Gap Semiconductor Sc2_{2}Si2_{2}Te6_{6}

Crystals of Sc$_{2}$Si$_{2}$Te$_{6}$ have been grown and its crystal, micro- and electronic structures were investigated. The layered character of the title compound exhibits stacking faults that impede a full structural characterization by single crystal X-ray diffraction due to diffuse scattering. Based on high resolution transmission electron micrographs and diffraction patterns, the stacking faulted nature of the real structure of Sc$_{2}$Si$_{2}$Te$_{6}$ has been revealed. Different stacking models were derived from the idealized, faultless structure and the stacking disorder was quantitatively analyzed by Rietveld refinement of powder X-ray diffraction patterns. An energetic comparison of the stacking models by density functional theory is in line with the experimental observations. Further, the bonding situation was investigated by electronic structure calculations. Sc$_{2}$Si$_{2}$Te$_{6}$ is a narrow gap semiconductor with an indirect band gap of 0.65 eV

Vanishing of phase coherence in underdoped Bi_2Sr_2CaCu_2O_8+d

Coherent time-domain spectroscopy is used to measure the screening and dissipation of high-frequency electromagnetic fields in a set of underdoped Bi_2Sr_2CaCu_2O_8+d thin films. The measurements provide direct evidence for a phase-fluctuation driven transition from the superconductor to normal state, with dynamics described well by the Berezinskii-Kosterlitz-Thouless theory of vortex-pair unbinding.Comment: Nature, Vol. 398, 18 March 1999, pg. 221 4 pages with 4 included figure

Epigenetic regulation in neonatal ECFCs following intrauterine exposure to gestational diabetes

poster abstractGestational diabetes (GDM) complicates up to 10% of pregnancies. In addition to acute risks, the children of diabetic mothers have an increased risk of obesity, diabetes, and hypertension, starting in childhood. While the causes of this increased risk are unknown, previous studies in our lab have identified functional deficits in endothelial colony forming cells (ECFCs) isolated from the cord blood of GDM pregnancies. This study focused on identifying genes that have altered epigenetic modifications that result in abnormal mRNA and protein expression in ECFCs from the cord blood GDM pregnancies. The objective of this study was to identify mRNA expression and DNA methylation alterations in ECFCs that may help identify the causes of ECFC dysfunction following intrauterine exposure to GDM. ECFCs were obtained from control and GDM pregnancies. DNA, RNA, and protein samples were isolated in parallel from ECFCs. RNA microarray analysis using the Affymetrix Human 1.0 Gene Array was used to identify gene expression alterations in GDM ECFCs compared to control ECFCs. Genome-wide DNA methylation was assessed using an Infinium 450K Methylation Array for DNA samples at >450,000 CpG sites. Correlation analysis was performed to identify possible sites that have altered CpG methylation and RNA expression. RNA expression results were validated using qRT-PCR and western blotting. Bisulfite sequencing of genomic DNA from the ECFCs was performed to identify additional sites with altered methylation for regions not included in the DNA methylation array. Of the 28,000 genetic loci tested, 596 mRNAs were altered between control and GDM ECFCs (p<0.01). More stringent criteria identified 38 genes for further investigation by limiting analysis to genes that exhibited increased or decreased expression by at least 50%, with a p<0.01. PLAC8 was identified as being increased 5-fold by microarray analysis, a result which was confirmed in two cohorts by qRT-PCR and western blotting. Analysis of the methylation array and bisulfite sequencing results revealed 3 regions surrounding the transcriptional start site of PLAC8 gene whose CpG methylation negatively correlate with RNA expression in samples from control and GDM ECFCs. In contrast, a CpG island is fully unmethylated in both control and GDM ECFCs. The discovery of CpG sites whose methylation correlates with PLAC8 mRNA expression in ECFCs is consistent with the hypothesis that intrauterine exposure to GDM results in epigenetic changes. Analysis of methylation at this site could be used as a biomarker for children of mothers with GDM who may be at risk for disease later in life. Using bisulfite pyrosequencing, we are currently developing assays to quickly determine if methylation of the PLAC8 putative promoter region is altered in cord blood mononuclear cells obtained from GDM or healthy control pregnancies. We are also investigating the role of methylation in regulating PLAC8 RNA expression, determining if there is altered histone modifications and transcription factor binding in these regions, and examining other genes that may comprise a molecular signature of ECFC dysfunction

Sustained Solar H2 Evolution from a Thiazolo[5,4-d]thiazole-Bridged Covalent Organic Framework and Nickel-Thiolate Cluster in Wate

Solar hydrogen (H2) evolution from water utilizing covalent organic frameworks (COFs) as heterogeneous photosensitizers has gathered significant momentum by virtue of the COFs’ predictive structural design, long-range ordering, tunable porosity, and excellent light-harvesting ability. However, most photocatalytic systems involve rare and expensive platinum as the co-catalyst for water reduction, which appears to be the bottleneck in the development of economical and environmentally benign solar H2 production systems. Herein, we report a simple, efficient, and low-cost all-in-one photocatalytic H2 evolution system composed of a thiazolo[5,4-d]thiazole-linked COF (TpDTz) as the photoabsorber and an earth-abundant, noble-metal-free nickel-thiolate hexameric cluster co-catalyst assembled in situ in water, together with triethanolamine (TEoA) as the sacrificial electron donor. The high crystallinity, porosity, photochemical stability, and light absorption ability of the TpDTz COF enables excellent long-term H2 production over 70 h with a maximum rate of 941 μmol h–1 g–1, turnover number TONNi > 103, and total projected TONNi > 443 until complete catalyst depletion. The high H2 evolution rate and TON, coupled with long-term photocatalytic operation of this hybrid system in water, surpass those of many previously known organic dyes, carbon nitride, and COF-sensitized photocatalytic H2O reduction systems. Furthermore, we gather unique insights into the reaction mechanism, enabled by a specifically designed continuous-flow system for non-invasive, direct H2 production rate monitoring, providing higher accuracy in quantification compared to the existing batch measurement methods. Overall, the results presented here open the door toward the rational design of robust and efficient earth-abundant COF–molecular co-catalyst hybrid systems for sustainable solar H2 production in water