1 Crystal density

Spark ◽  
2019 ◽  
Author(s):  
Mohammad H. Keshavarz ◽  
Thomas M. Klapötke
Keyword(s):  
Crystal Density

Das Kilogramm im neuen SI

2020 ◽  
Vol 87 (4) ◽  
pp. 237-247
Author(s):  
Frank Härtig ◽  
Dorothea Knopf ◽  
Katharina Lehrmann
Keyword(s):  
X Ray ◽  
Density Method ◽  
Consensus Value ◽  
Crystal Density ◽  
Wenn Sich

ZusammenfassungAm 20. Mai 2019 hat die Generalkonferenz für Maße und Gewichte die Definition zur Darstellung der Einheiten grundlegend erneut. Die Einheit Kilogramm des Internationalen Einheitensystems (SI) stand besonders im Fokus, da vermutet wurde, dass sich die Masse des Internationalen Kilogramm Prototyps (IPK) über die Zeit ändert. Wie auch andere SI-Einheiten wird das Kilogramm nun nicht mehr durch einen weltweit einzigen physikalischen Körper dargestellt, sondern über physikalische Konstante. Auswirkungen auf industrielle oder gesellschaftliche Anwendungen hat die neue Definition nicht, auch wenn sich die Genauigkeit der nationalen Massenormale etwas verschlechtert hat. Die Chancen liegen dagegen in der Vielfalt, mit der das Kilogramm künftig dargestellt werden kann. Grundlage für die neue Realisierung bilden derzeit zwei Experimente, die „Kibble-Waage“ (Kibble-Balance: KB) und die „X-Ray Crystal Density Method“ (XRCD-Methode). Letztere basiert auf Kugeln aus monokristallinem isotopenangereichertem Silizium. Systematische Abweichungen zwischen den beiden Experimenten zeigen, dass eine dreistufige Übergangsphase notwendig ist, um die grundlegende Stabilität für die Weitergabe der Größe Masse zu gewährleisten. Der IPK und ein sogenannter Consensus Value (CV) spielen dabei eine besondere Rolle. Die gute Handhabbarkeit und Stabilität von Silizium haben dazu geführt, dass die in der XRCD-Methode verwendeten Siliziumkugeln in ihrer natürlichen Isotopenzusammensetzung auch als sehr stabile Massenormale eingesetzt werden.

On the influence of weak intermolecular interactions on the molecular crystal density of 1,3,5-triazine trinitroalkyl derivatives

2021 ◽  
Vol 57 (3) ◽  
pp. 266-273
Author(s):  
Kyrill Yu. Suponitsky ◽  
Aleksei A. Anisimov ◽  
Ivan V. Ananyev ◽  
Alexander A. Lashakov ◽  
Svetlana V. Osintseva ◽  
...  
Keyword(s):  
Intermolecular Interactions ◽  
Molecular Crystal ◽  
Weak Intermolecular Interactions ◽  
Crystal Density

Enhancement of Carbon Dioxide Adsorption by Lithium Decorating and Fullerene Encapsulating in Metal-Organic Frameworks

2013 ◽  
Vol 773 ◽  
pp. 927-931
Author(s):  
Rui Feng Lu ◽  
De Wei Rao ◽  
Zhao Shun Meng ◽  
Kai Ming Deng
Keyword(s):  
Metal Organic Frameworks ◽  
Carbon Dioxide Adsorption ◽  
Grand Canonical Monte Carlo ◽  
Ambient Conditions ◽  
Li Doping ◽  
Lithium Doping ◽  
Crystal Density ◽  
Metal Organic ◽  
Density Surface ◽  
Grand Canonical

Using grand canonical Monte Carlo method, the capacities of CO2adsorption in IRMOF-12 and-14 are simulated at ambient conditions. We have theoretically found that CO2uptake can be greatly enhanced by either lithium doping or fullerene impregnating, and the influence of the Li doping is more significant than that of C60impregnation. Furthermore, the CO2storage capacities of IRMOFs after both Li doping and C60impregnating are improved to be about 30 times those of corresponding pristine structures. To further understand the mechanism, we analyzed the distribution pattern of CO2adsorption in materials and investigated the relationships between CO2uptakes and crystal density, surface area per volume and per mass, and pore volume per volume and per mass in detail.

Crystal density predictions for nitramines based on quantum chemistry

2007 ◽  
Vol 141 (1) ◽  
pp. 280-288 ◽  
Author(s):  
Ling Qiu ◽  
Heming Xiao ◽  
Xuedong Gong ◽  
Xuehai Ju ◽  
Weihua Zhu
Keyword(s):  
Quantum Chemistry ◽  
Crystal Density

Synthesis and structural characteristics of lithocholate triads: steroid-type channels occupied by spacer fragments

2008 ◽  
Vol 64 (3) ◽  
pp. 383-392 ◽  
Author(s):  
Urszula Rychlewska ◽  
Beata Warżajtis ◽  
Roman Joachimiak ◽  
Zdzisław Paryzek
Keyword(s):  
Inclusion Complexes ◽  
Terephthalic Acid ◽  
Lithocholic Acid ◽  
Structural Characteristics ◽  
Guest Molecules ◽  
Face To Face ◽  
Bifunctional Molecules ◽  
Hydrogen Bond Interactions ◽  
Crystal Density ◽  
Efficient Packing

Reported in this paper are the syntheses and X-ray investigations of C 2 symmetrical molecular A—B—A triads consisting of two steroid units (lithocholic acid or its methyl ester) joined together by linkers derived from bifunctional molecules such as terephthalic acid or N,N′-dicarboxypiperazine. Unlike their monomeric analogues, some of these compounds form inclusion complexes. All steroidal triads form crystals that are highly pseudo-centrosymmetric, in which the constituting molecules are held together either exclusively by van der Waals forces or form lattice inclusion complexes, with guest molecules hydrogen bonded to the host. The presence of carboxyl groups promotes the inclusion of pyridine molecules and the formation of the well known carboxylic acid...pyridine hydrogen bonds. Combined with pairwise face-to-face π-stacking between pyridine rings, these hydrogen-bond interactions lead to the formation of extended supramolecular tapes, analogous to polymers. The co-crystals of pyridine and a lithocholic acid triad undergo a symmetry-lowering phase transition from a P1 cell with Z = 1 to a P1 cell with Z = 2. The two structures are virtually the same, the two independent molecules in the larger cell being related by pseudo-translation. Changes in the type of spacer between two methyl lithocholate units from planar aromatic (terephthalic acid) to highly puckered aliphatic six-membered ring (N,N′-dicarboxypiperazine) bring about inclusion properties and changes in side-chain conformation in a crystal. Although the efficient packing of these highly elongated molecules is hindered, as indicated by low values of crystal density, ranging from 1.16 to 1.19 g cm−3, several very short C...O and H...H contacts are present in the crystals.

scholarly journals Examination of corneal deposits in nephropathic cystinosis using in vivo confocal microscopy and anterior segment optical coherence tomography: an age-dependent cross sectional study

2020 ◽  
Vol 20 (1) ◽  
Author(s):  
Anita Csorba ◽  
Erika Maka ◽  
Otto Alexander Maneschg ◽  
Attila Szabó ◽  
Nóra Szentmáry ◽  
...  
Keyword(s):  
Optical Coherence Tomography ◽  
Confocal Microscopy ◽  
Anterior Segment ◽  
Interquartile Range ◽  
Nephropathic Cystinosis ◽  
Optical Coherence ◽  
In Vivo Confocal Microscopy ◽  
Crystal Deposition ◽  
Crystal Density

Abstract Background Presence of corneal cystine crystals is the main ocular manifestation of cystinosis, although controversial findings concerning the corneal layer with the highest density have been reported. The aim of this study was the analysis of the characteristics of crystal arrangement in different corneal layers and the assessment of corneal morphological changes with age. Methods A cross sectional study was carried out in three children and three adults who had nephropathic cystinosis and corneal cystine depositions. All patients underwent a comprehensive ophthalmological examination including best corrected distance visual acuity, slit-lamp examination, in vivo confocal microscopy and anterior segment optical coherence tomography. An evaluation of the depth of crystal deposits and crystal density in different corneal layers was also performed. Due to the low number of subjects no statistical comparison was performed. Results Anterior segment optical coherence tomography images revealed deposition of hyperreflective crystals from limbus to limbus in each patient. Crystals appeared as randomly oriented hyperreflective, elongated structures on in vivo confocal microscopy images in all corneal layers except the endothelium. In children the deposits occurred predominantly in the anterior stroma, while in adults, the crystals were mostly localized in the posterior corneal stroma with the depth of crystal deposition showing an increasing tendency with age (mean depth of crystal density was 353.17 ± 49.23 μm in children and it was 555.75 ± 25.27 μm in adults). Mean crystal density of the epithelium was 1.47 ± 1.17 (median: 1.5; interquartile range: 0.3–2.4). Mean crystal density of the anterior and posterior stroma of children and adults was 3.37 ± 0.34 (median: 3.4; interquartile range: 3.25–3.55) vs. 1.23 ± 0.23 (median: 1.2; interquartile range: 1.05–1.35) and 0.76 ± 0.49 (median: 0.7; interquartile range: 0.4–1.15) vs. 3.63 ± 0.29 (median: 3.7; interquartile range: 3.45–3.8), respectively. Endothelium had intact structure in all cases. Some hexagonal crystals were observed in two subjects. Conclusions In vivo confocal microscopy and anterior segment optical coherence tomography confirmed an age-related pattern of crystal deposition. In children, crystals tend to locate anteriorly, while in adults, deposits are found posteriorly in corneal stroma.

scholarly journals Terapi Ammonium Khlorida-Asam Askorbat untuk Menurunkan Tingkat Keasaman Urin dan Kristalisasi Struvit pada Kucing Urolithiasis (THERAPY AMMONIUM CHLORIDE-ASCORBIC ACID FOR LOWERING URINE ACIDITY AND STRUVITE CRYSTALLIZATION IN FELINE UROLITHIASIS)

2019 ◽  
Vol 20 (1) ◽  
pp. 8
Author(s):  
Alfarisa Nururrozi ◽  
Soedarmanto Indarjulianto ◽  
Yanuartono Yanuartono ◽  
Hary Purnamaningsih ◽  
Sitarina Widyarini ◽  
...  
Keyword(s):  
Ascorbic Acid ◽  
Ammonium Chloride ◽  
Ammonium Phosphate ◽  
X Rays ◽  
Urine Ph ◽  
Magnesium Ammonium Phosphate ◽  
Activity Product ◽  
Crystal Density ◽  
Magnesium Ammonium ◽  
Struvite Crystallization

Struvite/Magnesium ammonium phosphate (MAP) is common causes of feline urolithiasis. Prevent the formation of MAP crystallization can be treated by adjusting the pH urine in acid conditions. Urine with an acid pH will decrease struvite activity product (SAP) by preventing the phosphate deprotonation process which is the main constituent of struvite components. This study aims to determine the potential of a combination of ammonium chloride (NH4Cl) and ascorbic acid to decrease SAP by retain the urine pH under normal conditions. Twelve male cats, 2-5 years old and body weight 3.0 ± 0.8 kg were diagnosed struvite urolithiasis used for this study. Cats have a9clinical history of hematuria, dysuria, polyuria, and stranguria. Diagnosis of urolithiasis performed by clinical examination, USG, x-rays, and urinalysis. Cats that found struvite urolith, treated with 200 mg/kg NH4Cl and 100 mg/kg ascorbic acid orally twice a day. The research objects were observed included urine pH and crystaluria density. The data were analyzed using analisis of varian. The result of this study showed NH4Cl and ascorbic acid treatment can decrease the urine pH at 8 cats (89%) with an average pH 6.3 ± 0.3. Microscopic examination of the urine showed the struvite crystallization more infrequently than before therapy. The study concluded that the combination of NH4Cl and asam askorbat can lower the urine pH and reduce struvite crystal density in the urine.

scholarly journals Tetrakis(2,3,5,5-tetramethylhexen-2-yl)silane

2014 ◽  
Vol 70 (3) ◽  
pp. o376-o376
Author(s):  
Frank Meyer-Wegner ◽  
Michael Bolte ◽  
Hans-Wolfram Lerner
Keyword(s):  
Double Bond ◽  
Title Compound ◽  
Crystal Packing ◽  
Site Symmetry ◽  
Asymmetric Unit ◽  
Special Position ◽  
Compound C ◽  
Butyl Group ◽  
Crystal Density ◽  
Short Contacts

In the title compound, C40H76Si, the Si atom is located on a special position of site symmetry -4. Thus, there is just a quarter of a molecule in the asymmetric unit. The C=C double bonds exhibit atransconfiguration. The Si atom and thetert-butyl group are located on the same side of the plane formed by the C=C double bond and its four substituents. The crystal packing shows no short contacts between the molecules and despite the low crystal density (0.980 Mg m−3), there are no significant voids in the structure.

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