A fast low-pressure transport route to large black phosphorus single crystals

Black phosphorus, a promising candidate for lithium battery electrodes, can be prepared by a low-pressure transport reaction route representing the first effective and scalable access to this element modification. Crystal sizes larger than 1 cm were obtained at low-pressure conditions in silica ampoules. X-ray phase analyses, EDX, ICP-MS and optical microscopy were applied to characterize the resulting black phosphorus. The present method drastically improves the traditional preparation ways like mercury catalysis, bismuth-flux or high-pressure techniques and represents an easy, non-toxic, fast and highly efficient method to achieve black phosphorus. In contrast to a previously reported low-pressure route the present transport reaction allows an up-scaling to higher masses of starting materials, a larger black phosphorus yield and faster reaction time under retention of the high product crystallinity.     

Second-order linearity of the general signed-rank statistic

Let X₁,…, X_n be i.i.d. random variables symmetric about zero. Let R_i(t) be the rank of |X_i − tn^−1/2| among |X₁ − tn^−1/2|,…, |X_n − tn^−1/2| and T_n(t) = Σ_{i = 1}ⁿφ((n + 1)⁻¹R_i(t))sign(X_i − tn^−1/2). We show that there exists a sequence of random variables V_n such that sup_{0 ≤ t ≤ 1} |T_n(t) − T_n(0) − tV_n| → 0 in probability, as n → ∞. V_n is asymptotically normal.     

Fifty Years of Inorganic Biomimetic Chemistry: From the Complexation of Single Metal Cations to Polynuclear Metal Complexes by Multidentate Thiolate Ligands

This article covers 50 years of coordination chemistry of transition metal complexes and metal-sulfur aggregates involving thiolate-incorporating ligands by reviewing selected examples. The studies in the coordination chemistry of sulfur-rich ligands have been undoubtedly triggered and fed by the concomitant development of bioinorganic chemistry, particularly of iron-sulfur enzymes. The review is broken down in five sections, which examine complexes of increasing nuclearity, including binuclear complexes based on compartmental macrocyclic ligands. We show also how ligand engineering has allowed the researchers in the field to control the nuclearity of the complexes, which was a particularly difficult task for sulfur-based ligands, as thiolates show a strong tendency to coordinate to more than one metal cation at once.     

Über Pterinchemie. 90. Mitteilung. Synthese und Kristallstruktur des ersten chinoiden Dihydropterinmolybdän (IV)-Komplexes

Synthesis and Crystal Structure of the First Quinoid Dihydropterinmolybdenum (IV) Complex The first molybdenum(IV) complex with a quinoid dihydropterin, i.e. 2 , was isolated and characterized by IR, UV and NMR data and single-crystal X-ray diffraction. The reaction of Mo^VIO₂Cl₂ with the biologically important 6β-5,6,7,8-tetrahydro-L-biopterin(²) ( 7 ) in MeOH gave almost quantitatively trichloro(1,5-quinoid-7,8-dihydro-6H-L-biopterin)oxomolybdenLim(IV) ( 2 ). The complex crystallizes with one molecule of MeOH in the noncentrosymmetric orthorhombic space group P2₁2₁2₁ (No. 19) with unit cell dimensions a = 1009.3(3), b = 1104.7(3), and c = 1484.5(4) pm and Z = 4. The Mo-atom has a distorted octahedral geometry (Fig.1). It is coordinated by N(5) and O(4) of the pterin ligand. The distance of the Mo–N(5) bond (202 pm) is unusually short compared to similar complexes. O(4) is located trans to a terminal oxo ligand. The octahedral coordination is completed by three Cl-atoms in a meridional arrangement. Complex 2, with the Mo-atom in the enzyme-relevant oxidation state +IV and the pterin in the intermediate quinoid dihydro form, should lead to an extension of the proposed ‘common molybdenum cofactor’ model.     

Eigenvalue and Eigenvector Analysis of Stability for a Line of Traffic

Many authors have recognized that traffic under the traditional car‐following model (CFM) is subject to flow instabilities. A recent model achieves stability using bilateral control (BCM)—by looking both forward and backward [1]. (Looking back may be difficult or distracting for human drivers, but is not a problem for sensors.) We analyze the underlying systems of differential equations by studying their eigenvalues and eigenvectors under various boundary conditions. Simulations further confirm that bilateral control can avoid instabilities and reduce the chance of collisions.     

Truthful mechanism design via correlated tree rounding

A powerful algorithmic technique for truthful mechanism design is the maximal-in-distributional-range (MIDR) paradigm. Unfortunately, many such algorithms use heavy algorithmic machinery, e.g., the ellipsoid method and (approximate) solution of convex programs. In this paper, we present a correlated rounding technique for designing mechanisms that are truthful in expectation. It is elementary and can be implemented quickly. The main property we rely on is that the domain offers fractional optimum solutions with a tree structure. In auctions based on the generalized assignment problem, each bidder has a publicly known knapsack constraint that captures the subsets of items that are of value to him. He has a private valuation for each item and strives to maximize the value of assigned items minus payment. For this domain we design a truthful 2-approximate MIDR mechanism for social welfare maximization. It avoids using the ellipsoid method or convex programming. In contrast to some previous work, our mechanism achieves exact truthfulness. In restricted-related scheduling with selfish machines, each job comes with a public weight, and it must be assigned to a machine from a public job-specific subset. Each machine has a private speed and strives to maximize payments minus workload of jobs assigned to it. Here we design a mechanism for makespan minimization. This is a single-parameter domain, but the approximation status of the optimization problem is similar to unrelated machine scheduling: The best known algorithm obtains a (non-truthful) 2-approximation for unrelated machines, and there is 1.5-hardness. Our mechanism matches this bound with a truthful 2-approximation.     

Nuclear coherences in photosynthetic reaction centers following light excitation

Transient electron paramagnetic resonance is used to study the secondary radical pair in plant photosystem I. Nuclear coherences are observed in the transverse magnetization at lower temperatures following light excitation. Comparative studies of deuterated and deuterated¹⁵N-substituted cyanobacteriaS. lividus indicate assignment of these coherences to nitrogen nuclei in the primary donor and deuterons in the secondary acceptor. The modulation amplitude of a deuteron matrix line, as a function of the microwave power, reveals a distinct resonance behavior. The maximum amplitude is obtained when the Rabi frequency equals the nuclear Zeeman frequency.     

Relative elemental sensitivity factors in non-resonant laser-SNMS

Using a reflectron time-of-flight mass spectrometer, the ionization process in non-resonant Laser postionization Secondary Neutral Mass Spectrometry (SNMS) has been investigated. In particular, the postionization efficiencies (PIE) achieved by multi photon and single photon absorption have been compared by ionizing ten elements sputtered from a NIST standard reference material by excimer laser radiation of 248 nm, 193 nm and 157 nm. Only in the case of single photon ionization (SPI) the measured laser intensity dependence of the PIE can be understood quantitatively in terms of corresponding theory. From the results, absolute values of the SPI cross sections have been evaluated for atoms of nine elements, which show a total variation over about two orders of magnitude. Furthermore, even in the regime of high laser intensity, where the ionization of all atoms is completely saturated, different elements have been detected with relative sensitivity factors which scatter over about one order of magnitude. This has been attributed to element dependent variations of the effective ionization volume which are caused by the different kinetic energy and angular distributions of different sputtered atoms.