Leibniz University of Hanover

About: Leibniz University of Hanover is a education organization based out in Hanover, Niedersachsen, Germany. It is known for research contribution in the topics: Finite element method & Computer science. The organization has 14283 authors who have published 29845 publications receiving 682152 citations.

A Two-Dimensional Lamellar Membrane: MXene Nanosheet Stacks

Abstract: Two-dimensional (2D) materials are promising candidates for advanced water purification membranes. A new kind of lamellar membrane is based on a stack of 2D MXene nanosheets. Starting from compact Ti3AlC2, delaminated nanosheets of the composition Ti3C2Tx with the functional groups T (O, OH, and/or F) can be produced by etching and ultrasonication and stapled on a porous support by vacuum filtration. The MXene membrane supported on anodic aluminum oxide (AAO) substrate shows excellent water permeance (more than 1000 L m−2 h−1 bar−1) and favorable rejection rate (over 90 %) for molecules with sizes larger than 2.5 nm. The water permeance through the MXene membrane is much higher than that of the most membranes with similar rejections. Long-time operation also reveals the outstanding stability of the MXene membrane for water purification.

Functions of Macronutrients

Abstract: Publisher Summary This chapter focuses on the role played by various macronutrients such as nitrogen (N), sulfur (S), phosphorus (P), magnesium (Mg), calcium (Ca), and potassium (K) in plant metabolism and growth and describes the symptoms of deficiency and toxicity of these macronutrients. N is the most essential element required after carbon, and it plays a central role in plant metabolism as a constituent of proteins, nucleic acids, chlorophyll, coenzymes, phytohormones, and secondary metabolites. When it is taken as ammonium or nitrate, it is assimilated into amino acids either in the roots or shoots and within the plant, it is translocated as nitrate or amino acids. Sulfur is taken up as sulphate and assimilated into S-containing amino acids such as cysteine that are used to synthesize S-containing enzymes and coenzymes as well as secondary compounds such as phytochelatins (detoxification of metals) or aliins and glucosinolates (feeding deterrents). Phosphorus is a structural element in nucleic acids, and as a component of adenosine phosphates, it plays an important role in energy transfer, and it is also essential for transfer of carbohydrates in leaf cells. Magnesium is a component of chlorophyll, and it is required for photosynthesis and protein synthesis. Calcium is important for cell wall and membrane stabilization, osmoregulation, and as second messenger, thereby allowing plants to regulate developmental processes in response to environmental stimuli. The main role of K is osmoregulation, which is important for cell extension and stomata movement, and it affects loading of sucrose and the rate of mass flow-driven solute movement within the plant.

Astrophysical implications of the binary black hole merger gw150914

Abstract: The discovery of the gravitational-wave source GW150914 with the Advanced LIGO detectors provides the first observational evidence for the existence of binary black-hole systems that inspiral and merge within the age of the Universe. Such black-hole mergers have been predicted in two main types of formation models, involving isolated binaries in galactic fields or dynamical interactions in young and old dense stellar environments. The measured masses robustly demonstrate that relatively "heavy" black holes (≳25M⊙) can form in nature. This discovery implies relatively weak massive-star winds and thus the formation of GW150914 in an environment with metallicity lower than ∼1/2 of the solar value. The rate of binary black-hole mergers inferred from the observation of GW150914 is consistent with the higher end of rate predictions (≳1Gpc−3yr−1) from both types of formation models. The low measured redshift (z∼0.1) of GW150914 and the low inferred metallicity of the stellar progenitor imply either binary black-hole formation in a low-mass galaxy in the local Universe and a prompt merger, or formation at high redshift with a time delay between formation and merger of several Gyr. This discovery motivates further studies of binary-black-hole formation astrophysics. It also has implications for future detections and studies by Advanced LIGO and Advanced Virgo, and gravitational-wave detectors in space.

MXene molecular sieving membranes for highly efficient gas separation.

Abstract: Molecular sieving membranes with sufficient and uniform nanochannels that break the permeability-selectivity trade-off are desirable for energy-efficient gas separation, and the arising two-dimensional (2D) materials provide new routes for membrane development. However, for 2D lamellar membranes, disordered interlayer nanochannels for mass transport are usually formed between randomly stacked neighboring nanosheets, which is obstructive for highly efficient separation. Therefore, manufacturing lamellar membranes with highly ordered nanochannel structures for fast and precise molecular sieving is still challenging. Here, we report on lamellar stacked MXene membranes with aligned and regular subnanometer channels, taking advantage of the abundant surface-terminating groups on the MXene nanosheets, which exhibit excellent gas separation performance with H2 permeability >2200 Barrer and H2/CO2 selectivity >160, superior to the state-of-the-art membranes. The results of molecular dynamics simulations quantitatively support the experiments, confirming the subnanometer interlayer spacing between the neighboring MXene nanosheets as molecular sieving channels for gas separation. Two-dimensional materials show great potential for membrane technologies, but their disordered channels hinder their molecular sieving performance. Here, Wang, Gogotsi and colleagues design a MXene membrane with ordered nanochannels that exhibits an excellent H2/CO2 gas separation performance.