Chemistry News

Raman Thermometry in Water, Ethanol, and Ethanol/Nitrogen Mixtures from Ambient to Critical Conditions

posted by ­김형민‎(응용화학과)‎


Figure

We present investigations into remote liquid temperature sensing with Raman spectroscopy using different evaluation methods for the OH stretching vibration band. Water, ethanol, and ethanol saturated with nitrogen, all as liquids or liquid-like supercritical fluids, are pumped through a heated microcapillary system at elevated pressures. Raman spectra are recorded from the liquid inside the microcapillary and are evaluated with respect to the temperature sensitivity of the OH stretching vibration. The four approaches applied are (i) to evaluate the center position of the Raman OH-band, (ii) the integrated absolute difference spectrum, (iii) the intensity ratio of two regions of the OH-band, and (iv) the intensity ratio of two fitted Gaussian peaks. The temperature range investigated covers from ambient temperature to the component’s respective boiling temperature or critical temperature at sub- and supercritical pressures. Precision and robustness of the employed methods are characterized. It is shown that two out of the four methods feature temperature deviations smaller than 5 K at all pressures and that one method can also be applied to liquid mixtures of ethanol and nitrogen. Applicability to other liquids and mixtures is discussed.

Energy Flux Manipulation in Upconversion Nanosystems

posted Jan 15, 2019, 6:12 AM by ­김형민‎(응용화학과)‎

Liang, L.; Qin, X.; Zheng, K.; Liu, X. Acc. Chem. Res. 2019, 52 (1), 228–236.

Lanthanide-doped upconversion nanoparticles (UCNPs) exhibit unique optical characteristics, including a large anti-Stokes shift, a long luminescence lifetime, sharp emission bands, and high photostability. These virtues make UCNPs highly useful in many emerging applications such as biolabeling, security, multicolor displays, and optogenetics. Despite the enticing prospects of UCNPs, their practical utility is greatly hindered by the low efficiency of the conversion from near-infrared (NIR) excitation to visible emission. In a typical nanosystem codoped with sensitizers and activators, upconversion processes occur through NIR light sensitization, energy transfer from sensitizers to activators, sequential energy population at the excited states of the activators, and eventually the release of higher-energy photons. In fact, in the upconversion nanosystem, each step in the energy flux, including NIR energy injection, energy transfer and migration, and energy dissipation, has a decisive effect on the resulting luminescence intensity. Important in-depth studies have been conducted in pursuit of brighter UCNPs. Specifically, lanthanide ions possessing larger absorption cross sections (Nd3+) or organic dye molecules have been chosen as NIR light sensitizers to improve the light harvesting ability of upconversion nanostructures. The doping concentration and spatial distribution of lanthanide ions are strictly managed to mitigate detrimental energy cross-talk processes. The surfaces of UCNPs are passivated with epitaxially grown layers to block surface quenching. Therefore, rational design of energy flux manipulation, through control of excitation energy collection, transmission, and release in a three-dimensional nanospace of UCNPs, is crucial in constructing nanosystems with high upconversion efficiencies.
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Why a postdoc might not advance your career

posted Jan 14, 2019, 6:10 AM by ­김형민‎(응용화학과)‎

https://www.nature.com/articles/d41586-018-07652-y

Of the 97 postdocs interviewed in 2016 and early 2017 for the Research Policy paper, 84 had originally planned to go on to an academic career. At the time of publication, five of those postdocs, or 6%, had in fact landed tenure-track positions, but many of the rest will eventually have to pursue other options, says lead author Christopher Hayter, a higher-education researcher at Arizona State University in Tempe. “It’s shocking when a postdoc at a top research institution can’t find a job in academia,” he says, “but that’s par for the course.”
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postdocs can have a hard time competing for non-academic jobs. One potential employer interviewed said that postdocs “have all the academic science skills you don’t need, and none of the organizational skills that you do”.
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A Decision by Scientists

posted Jan 14, 2019, 5:26 AM by ­김형민‎(응용화학과)‎   [ updated Jan 14, 2019, 5:26 AM ]

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The real problem, however, is that by doing what he did, He appropriated responsibility for a decision that belongs to all of us. Scientific leaders now risk repeating the same error. To move forward in a positive direction, science must not presume to set the destination for a technology, but should follow the direction that we, the people, provide. Science is — and must be — in the service of the societies of which it is part.
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As US Senator Edward Kennedy remarked: “They were making public policy. And they were making it in private.” This allowed research to proceed, but at the price of public trust.
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Why is Milk White?

posted Jan 7, 2019, 5:49 AM by ­김형민‎(응용화학과)‎   [ updated Jan 7, 2019, 6:40 AM ]

https://www.compoundchem.com/2018/06/02/milk/



The fat has a lower density than water, so if the milk is left to stand it floats to the top, and can be skimmed off. This gives skimmed milk.

n milk, proteins form structures called micelles. The micelles are on average about 150 nanometres in diameter, and this very small size means they are able to scatter light that hits them. The overall effect of this scattering by the huge number of micelles in milk is that it looks white.

Lactose is a sugar found only in milk and dairy products. In our bodies, the enzyme lactase breaks it down into two smaller sugars, galactose and glucose. However, some people don’t produce enough lactase for this enzymatic breakdown to happen – these people are lactose intolerant. In their digestive systems, lactose passes through unchanged, and eventually reaches the colon. There, bacteria break it down, producing gas which can cause discomfort.


What Do Milk Fat Percentages Mean?


per 1 oz = 1/16 lb = 28.35 g

When you shop in the dairy case, the primary types of milk available are whole milk (3.25% milk fat), reduced-fat milk (2%), lowfat milk (1%) and fat free milk, also known as skim milk.

What Is Half-and-Half Made Of? Half-and-half, also known as half cream in the United Kingdom, is a simple blend of equal parts whole milk and light cream. It averages 10 to 12% fat, which is more than milk but less than light cream. Due to its lower fat content than cream, it can't be whipped. (https://www.thekitchn.com/what-is-halfandhalf-ingredient-intelligence-205959)

Autofluorescence spectroscopy of epithelial tissues

posted Dec 19, 2018, 1:10 PM by ­김형민‎(응용화학과)‎

AAutofluorescence of rabbit and human epithelial tissues were studied by using a depth-resolved fluorescence spectroscopy system with multiple excitations. Keratinization was found to be common in the squamous epithelium. Strong keratin fluorescence with excitation and emission characteristics similar to collagen were observed in the topmost layer of the keratinized squamous epithelium. The keratin signal created interference in the assessment of the endogenous fluorescence signals .NADH/FAD fluorescence in epithelium and collagen fluorescence in stroma. associated with the development of epithelial precancer. Furthermore, the keratinized epithelial layer attenuated the excitation light and reduced the fluorescence signals from underlying tissue layers. The autofluorescence of columnar epithelium was found to be dominated by NADH and FAD signals, identical to the autofluorescence measured from nonkeratinized squamous epithelium. The study also demonstrated that a fluorescence signal excited at 355 nm produced sufficient contrast to resolve the layered structure of epithelial tissue, while the signal excited at 405 nm provided the information for a good estimation of epithelial redox ratios that are directly related to tissue metabolism. Overall, the depth-resolved measurements are crucial to isolate the fluorescence signals from different sublayers of the epithelial tissue and provide more accurate information for the tissue diagnosis.

Hand-Held AO Ophthalmoscopy Enables Cellular-Level Imaging

posted Nov 16, 2018, 7:39 AM by ­김형민‎(응용화학과)‎

Advancements in adaptive optics and ophthalmic imaging are facilitating the visualization of the
human retina and providing researchers with an expanded understanding of eye health and disease.
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AO was first used in astronomical telescopes to reduce wavefront distortions induced by atmospheric turbulence. Its applications have expanded to find utility in ophthalmic imaging, high-power lasers, vision research, and microscopy.

https://www.biophotonics-digital.com/biophotonics/november_december_2018/



Concentration Quenching in Upconversion Nanocrystals

posted Nov 16, 2018, 7:16 AM by ­김형민‎(응용화학과)‎

https://pubs.acs.org/doi/10.1021/acs.jpcc.8b09371

Abstarct
Despite considerable effort to improve upconversion (UC) in lanthanide-doped nanocrystals (NCs), the maximum reported efficiencies remain below 10%. Recently, we reported on low Er3+- and Yb3+-doped NaYF4 NCs giving insight into fundamental processes involved in quenching for isolated ions. In practice, high dopant concentrations are required and there is a trend toward bright UC in highly doped NCs. Here, additional quenching processes due to energy transfer and migration add to a reduction in UC efficiency. However, a fundamental understanding on how concentration quenching affects the quantum efficiency is lacking. Here, we report a systematic investigation on concentration-dependent decay dynamics for Er3+ or Yb3+ doped at various concentrations (1−100%) in core and core−shell NaYF4 NCs. The qualitative and quantitative analyses of luminescence decay curves and emission spectra show strong concentration quenching for the green emitting Er3+ 4S3/2 and NIR-emitting 4I11/2 levels, whereas concentration quenching for the red-emitting 4F9/2 level and the IR emitting 4I13/2 level is limited. The NIR emission of Yb3+ remains efficient even at concentration as high as 60% Yb3+, especially in core−shell NCs. Finally, the role of solvent quenching was investigated and reveals a much stronger quenching in aqueous media that can be explained by the high-energy O−H vibrations. The present study uncovers a more complete picture of quenching processes in highly doped UC NCs and serves to identify methods to further optimize the efficiency by careful tuning of lanthanide concentrations and core−shell design.

WINNERS OF THE 2019 BREAKTHROUGH PRIZE IN LIFE SCIENCES, FUNDAMENTAL PHYSICS AND MATHEMATICS ANNOUNCED

posted Oct 18, 2018, 7:18 AM by ­김형민‎(응용화학과)‎

A Total of $22 Million Awarded for Breakthroughs in Treatment for the Leading Genetic Cause of Infant Death, Super-Resolution Imaging, Discovery of a New Kind of Electronic Material, and Other Major Achievements. 
2019 Breakthrough Prize in Life Sciences Awarded to C. Frank Bennett and Adrian R. Krainer, Angelika Amon, Xiaowei Zhuang, and Zhijian “James” Chen. 
2019 Breakthrough Prize in Fundamental Physics Awarded to Charles Kane and Eugene Mele.
2019 Breakthrough Prize in Mathematics Awarded to Vincent Lafforgue. 
Six “New Horizons” Prizes Worth $600,000 Awarded for Early-Career Achievement in Physics and Math. 



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