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Arthur Baragar 《Geometriae Dedicata》2018,195(1):137-161
The Apollonian circle and sphere packings are well known objects that have attracted the attention of mathematicians throughout the ages. The historically natural generalization of the procedure for generating the packing breaks down in higher dimensions, as it leads to overlapping hyperspheres. There is, however, an alternative interpretation that allows one to extend the concept to higher dimensions and in a unique way. For relatively small dimensions (2 through at least 8), those packings can be thought of as ample cones for classes of K3 surfaces. We describe the packings in some detail for dimensions 4 (with plenty of pictures), 5, and 6. 相似文献
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Karen A. Gonzalez Sarah Kazemeini Dustyn C. Weber Paula A. Cordero Elizabeth M. Garcia Cory A. Rusinek 《Electroanalysis》2023,35(9):e202300098
Trace metals are required in the body as they play a significant role in several biochemical processes. Moreover, certain heavy metals are beneficial at appropriate levels. Copper (Cu), for example, is essential for red blood cell formation, bone strength, and infant growth. Despite these fundamental roles, Cu can become toxic at high levels. Other heavy metals such as lead (Pb), cadmium (Cd), manganese (Mn), and mercury (Hg), have been identified to cause acute and chronic health complications. For these reasons, rapid, real-time quantification of such metals in biological media is of interest to improving human health outcomes. Electrochemical methods offer numerous advantages, such as portability, capability to be miniaturized, low cost, and ease-of-use. In this review, we examine recent developments in electrochemical sensing for the detection of heavy metals in biological media. To meet the requirements for inclusion in this review, the electrochemical sensor must have been evaluated in biological media (blood, serum, sweat, saliva, urine, brain tissue/cells). Several applications are explored to examine recent advancements in electrochemical sensing within these matrices. Addressing the challenges through materials, device, and system innovations, it is expected that electrochemical sensing of heavy metals in biological media will facilitate future diagnoses and treatments in healthcare. 相似文献
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The Reaction of Cs2[Tc(NO)F5] with BF3 in Acetonitrile: Formation and Structure of [{Tc(NO)(CH3CN)4}2(μ‐F)](BF4)3 下载免费PDF全文
Samundeeswari Mariappan Balasekaran Adelheid Hagenbach Johann Spandl Ulrich Abram 《无机化学与普通化学杂志》2017,643(18):1146-1149
The deep blue, paramagnetic Cs2[TcII(NO)F5] is formed during reactions of pertechnetate, acetohydroxamic acid, and CsF in aqueous HF. A reaction of Cs2[Tc(NO)F5] with BF3 · MeOH in acetonitrile gives yellow blocks of the fluorido‐bridged dimer [{TcI(NO)(CH3CN)4}2F](BF4)3. The compound is stable as solid and in acetonitrile solutions. The complex cation contains a bent μ‐F– ligand and two linear nitrosyl groups. 相似文献
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N. Gharibyan B. J. Bene R. Sudowe 《Journal of Radioanalytical and Nuclear Chemistry》2017,311(1):179-187
The impact of various ion chromatography parameters on the separation of trace amounts of thulium from erbium was examined to address the need for the preparation of a 171Tm target for neutron capture cross section measurements. The following optimal operation parameters for analytical scale separations with cation exchange resin were established based on a modified separation resolution: 0.046 M α-HIB? as eluent with a flow rate of 1.2 mL min?1 at 25 °C. Different carboxylic acids with varying pH were also investigated, which reaffirmed the use of α-hydroxyisobutyrate as the most suitable complexant for the separation of these neighboring lanthanides. 相似文献
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Pradip K. Bhowmik Tae S. Jo Jung J. Koh Jongwon Park Bidyut Biswas Ronald Carlo G. Principe Haesook Han Andrs F. Wacha Matti Knaapila 《Molecules (Basel, Switzerland)》2021,26(6)
A series of poly(pyridinium salt)s-fluorene main-chain ionic polymers with various organic counterions were synthesized by using ring-transmutation polymerization and metathesis reactions. Their chemical structures were characterized by Fourier Transform Infrared (FTIR), proton (1H), and fluorine 19 (19F) nuclear magnetic resonance (NMR) spectrometers. These polymers showed a number-average molecular weight (Mns) between 96.5 and 107.8 kg/mol and polydispersity index (PDI) in the range of 1.12–1.88. They exhibited fully-grown lyotropic phases in polar protic and aprotic solvents at different critical concentrations. Small-angle X-ray scattering for one polymer example indicates lyotropic structure formation for 60–80% solvent fraction. A lyotropic smectic phase contains 10 nm polymer platelets connected by tie molecules. The structure also incorporates a square packing motif within platelets. Thermal properties of polymers were affected by the size of counterions as determined by differential scanning calorimetry and thermogravimetric analysis measurements. Their ultraviolet-visible (UV-Vis) absorption spectra in different organic solvents were essentially identical, indicating that the closely spaced π-π* transitions occurred in their conjugated polymer structures. In contrast, the emission spectra of polymers exhibited a positive solvatochromism on changing the polarity of solvents. They emitted green lights in both polar and nonpolar organic solvents and showed blue light in the film-states, but their λem peaks were dependent on the size of the counterions. They formed aggregates in polar aprotic and protic solvents with the addition of water (v/v, 0–90%), and their λem peaks were blue shifted. 相似文献
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Nicholas A. Smith Gary S. Cerefice Kenneth R. Czerwinski 《Journal of Radioanalytical and Nuclear Chemistry》2013,295(2):1553-1560
Near real time process monitoring of the uranium content in an aqueous fuel recycling plant is a desired component of an advanced safeguards suite; Ultraviolet–Visible spectroscopy and Time Resolved Laser induced Fluorescence Spectroscopy can contribute to this technology gap. This work presents the observation of the spectroscopic parameters (molar absorptivities, fluorescent response) of the uranyl ion across the range of conditions expected in reprocessing chemistry. From this data, a monitor using the ratio of the absorbance of the uranyl ion at 403 and 426 nm has been developed. This technique can determine the nitrate solution concentration and can be coupled with a condition appropriate molar absorptivity to determine the uranyl concentration. This method provides a reliable technique for online, real time process monitoring of the uranyl and nitrate concentration under a wide range of solution compositions. 相似文献
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