Die Kristall- und Molekülstruktur von trans-Tetrazen-(2) (N4H4) bei -90°C

Die Kristallstruktur von trans-Tetrazen-(2), H2NNNNH2, wurde bei -90°C mit Hilfe der Röntgenstrukturanalyse über photometrische Filmtechniken bestimmt (CuK-Strahlung, 508 Reflexe, R = 0,12). Die Verbindung kristallisiert triklin in der Raumgruppe P mit den Gitterkonstanten: a = 1 023(3), b = 712(2), c = 419(2) pm, = 102,0(8), = 90,0(8), = 106,5(8)°. Nur verzwillingte Individuen mit (100) als Zwillingsebene konnten erhalten werden. Die Elementarzelle enthält vier kristallographisch unterschiedliche Moleküle der Punktsymmetrie (Ci). Die Tetrazeneinheiten sind über asymmetrische Wasserstoffbrücken (N H: 207 bis 263 pm bzw. für die entsprechenden N N-Abstände: 303 bis 342 pm) zu einem dreidimensionalen Netzwerk miteinander verbunden. Im Molekül sind an die trans-konfigurierte Azogruppe trigonal pyramidal koordinierte Stickstoffatome gebunden. Wichtige molekulare Größen (Mittelwerte aus den vier Einheiten) sind die kurze NN-Doppelbindung (120,5(1,6) pm), die NN-Einfachbindung mit 142,9(5) pm und der spitze NNN-Winkel von 109(2)°. Die Konformation der NH2-Gruppen zum Azosystem ist bei allen Molekülen pseudo-gauche, d. h. die einsamen Elektronenpaare des Amin- und des Azostickstoffatoms stehen streng orthogonal zueinander. Einige der geometrischen Details der Molekülstruktur können unter anderem auf die stereochemische Aktivität der einsamen Elektronenpaare an den sp2-hydridisierten Stickstoffatomen zurückgeführt werden. Erstmals können bei der Thermolyse von Tetrazen (bei unterschiedlichen Bedingungen) Ammoniumazid (NH4N3) und Hydraziniumazid (N2H5N3) als Zersetzungsprodukte röntgenographisch nachgewiesen werden

Cyclische Diazastannylene. - XV : Charakterisierung einer instabilen Zwischenstufe : 1,3-Di-tert-buty-2,2-dimethyl-4-tert-butyl-ammonium-1,3,2,4lambda 3-diazasila-stannetidin

Der Primärschritt in der Reaktion von 1,3-Di-tert-butyl-2,2-dimethyl-1,3,2,42-diazasilastannetidin (1) mit tert-Butylamin stellt die Bildung des Lewis-Säure-Base-Adduktes 5 dar. In 5 ist an das elektrophile Zinnatom von 1 das nukleophile Stickstoffatom des tert-Butylamins koordiniert. 5 kristallisiert unterhalb -110°C in einer triklinen Zelle mit folgenden Abmessungen (konventionelle Zelle s. Tab. 2): a = 1034(4), b = 1492(5), c = 654(3) pm, = 89,9(3), = 96,8(3), = 91,6(3)°, Z = 2. Oberhalb -110°C kann die trikline Phase von 5 in eine monokline (Raumgruppe: P21/m) umgewandelt werden, die bei -90°C folgende Gitterkonstanten aufweist: a = 1048(3), b = 1513(4), c = 654(2), = 96,9(3)°, Z = 2. Nach einer bei -90°C durchgeführten Röntgenstrukturanalyse an letzterer Phase besitzt die instabile Zwischenstufe 5 CS(m)-Punktsymmetrie. Wichtige molekulare Abmessungen sind die relativ lange SnN-Donorbindung von 242(3) pm, die SnN-Abstände im Ring von 211(2) pm sowie die trigonal-pyramidale Koordination am Zinnatom mit einem mittleren Winkel NSnN von 82,3°. Der Diazasilastannavierring weicht um 12° von der Planarität ab, wodurch die Stickstoffatome Spitzen flacher Pyramiden einnehmen. Diese Geometrie wird durch intramolekulare N···H-Kontakte (290 pm) der Amino-Wasserstoffatome mit den Stickstoffatomen des Ringes verursacht. Einige Folgerungen für den weiteren Reaktionsweg können aus der Struktur von 5 gezogen werden

Using an unmanned aerial vehicle to evaluate nitrogen variability and height effect with an active crop canopy sensor

Ground-based active sensors have been used in the past with success in detecting nitrogen (N) variability within maize production systems. The use of unmanned aerial vehicles (UAVs) presents an opportunity to evaluate N variability with unique advantages compared to ground-based systems. The objectives of this study were to: determine if a UAV was a suitable platform for use with an active crop canopy sensor to monitor in-season N status of maize, if UAV’s were a suitable platform, is the UAV and active sensor platform a suitable substitute for current handheld methods, and is there a height effect that may be confounding measurements of N status over crop canopies? In a 2013 study comparing aerial and ground-based sensor platforms, there was no difference in the ability of aerial and ground-based active sensors to detect N rate effects on a maize crop canopy. In a 2014 study, an active sensor mounted on a UAV was able to detect differences in crop canopy N status similarly to a handheld active sensor. The UAV/active sensor system (AerialActive) platform used in this study detected N rate differences in crop canopy N status within a range of 0.5–1.5 m above a relatively uniform turfgrass canopy. The height effect for an active sensor above a crop canopy is sensor- and crop-specific, which needs to be taken into account when implementing such a system. Unmanned aerial vehicles equipped with active crop canopy sensors provide potential for automated data collection to quantify crop stress in addition to passive sensors currently in use

Universality of the Collins-Soper kernel in lattice calculations

The Collins-Soper (CS) kernel is a nonperturbative function that characterizes the rapidity evolution of transverse-momentum-dependent parton distribution functions (TMDPDFs) and wave functions. In this Letter, we calculate the CS kernel for pion and proton targets and for quasi-TMDPDFs of leading and next-to-leading power. The calculations are carried out on the CLS ensemble H101 with dynamical $N_f=2+1$ clover-improved Wilson fermions. Our analyses demonstrate the consistency of different lattice extractions of the CS kernel for mesons and baryons, as well as for twist-two and twist-three operators, even though lattice artifacts could be significant. This consistency corroborates the universality of the lattice-determined CS kernel and suggests that a high-precision determination of it is in reach.Comment: 10 pages, 7 figures, published versio

Increased mortality in hematological malignancy patients with acute respiratory failure from undetermined etiology : a Groupe de Recherche en Réanimation Respiratoire en Onco-Hématologique (Grrr-OH) study

Background: Acute respiratory failure (ARF) is the most frequent complication in patients with hematological malignancies and is associated with high morbidity and mortality. ARF etiologies are numerous, and despite extensive diagnostic workflow, some patients remain with undetermined ARF etiology. Methods: This is a post-hoc study of a prospective multicenter cohort performed on 1011 critically ill hematological patients. Relationship between ARF etiology and hospital mortality was assessed using a multivariable regression model adjusting for confounders. Results: This study included 604 patients with ARF. All patients underwent noninvasive diagnostic tests, and a bronchoscopy and bronchoalveolar lavage (BAL) was performed in 155 (25.6%). Definite diagnoses were classified into four exclusive etiological categories: pneumonia (44.4%), non-infectious diagnoses (32.6%), opportunistic infection (10.1%) and undetermined (12.9%), with corresponding hospital mortality rates of 40, 35, 55 and 59%, respectively. Overall hospital mortality was 42%. By multivariable analysis, factors associated with hospital mortality were invasive pulmonary aspergillosis (OR 7.57 (95% CI 3.06-21.62); p 7 (OR 3.32 (95% CI 2.15-5.15); p < 0.005) and an undetermined ARF etiology (OR 2.92 (95% CI 1.71-5.07); p < 0.005). Conclusions: In patients with hematological malignancies and ARF, up to 13% remain with undetermined ARF etiology despite comprehensive diagnostic workup. Undetermined ARF etiology is independently associated with hospital mortality. Studies to guide second-line diagnostic strategies are warranted

Determination of the Collins-Soper Kernel from Lattice QCD

We present lattice results for the non-perturbative Collins-Soper (CS) kernel, which describes the energy-dependence of transverse momentum-dependent parton distributions (TMDs). The CS kernel is extracted from the ratios of first Mellin moments of quasi-TMDs evaluated at different nucleon momenta. The analysis is done with dynamical Nf = 2 + 1 clover fermions for the CLS ensemble H101 (a = 0.0854 fm, mπ = mK = 422 MeV). The computed CS kernel is in good agreement with experimental extractions and previous lattice studies