Remarkably volatile copper(II) complexes of N,N'-unsymmetrically substituted 1,3-diketimines as precursors for Cu metal deposition via CVD or ALD

To enhance the volatility of the copper precursor in the copper deposition process, it was envisioned that N,N'-unsymmetrically substituted 1,3-diketimines should be more volatile than their symmetrically substituted counterparts. A variety of Cu(II) (N,N'-unsymmetrically substituted 1,3-diketiminate) complexes have been synthesized and have proven to be much more volatile than their symmetrical counterparts. This makes the new materials particularly attractive to the ALD and CVD processes. Among the new compounds, 8-a and 8-b are sublimable even at room temperature.     

Proton-neutron excitations in the high-spin states of 95Tc

The high-spin states of ⁹⁵Tc have been studied in the reaction ⁹³Nb(α, 2n)⁹⁵Tc using inbeam spectroscopy of both γ-rays and conversion electrons. A new sequence of negative-parity states extending up to angular momentum $\text{I =}\text{29}\text{2}$ was found to exist within an excitation energy interval of 4.1 MeV. The positive-parity states are in remarkable agreement with the predictions of a simplified shell-model approach on the basis of coupled excitations of $\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ proton and $\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}{}^{\mathrm{?}}$ as well as $\text{g}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ neutron configurations. A similar analysis for the negative-parity states shows qualitative agreement with the experimental results.     

Tunable detection of high-frequency phonons in LaF3

Tunable detection of high-frequency phonons in LaF₃ is reported. Phonons generated by a heat-pulse technique are detected by phonon-induced fluorescence from magnetically split energy levels of Er³⁺ impurity ions. Evidence for a strongly frequency-dependent lifetime of acoustic phonons at frequencies above 600 GHz is found. The lifetime is attributed to spontaneous anharmonic phonon decay.     

A slow gravity compensated atom laser

We report on a slow guided atom laser beam outcoupled from a Bose–Einstein condensate of ⁸⁷Rb atoms in a hybrid trap. The acceleration of the atom laser beam can be controlled by compensating the gravitational acceleration and we reach residual accelerations as low as 0.0027 g. The outcoupling mechanism allows for the production of a constant flux of 4.5×10⁶ atoms per second and due to transverse guiding we obtain an upper limit for the mean beam width of 4.6 μm. The transverse velocity spread is only 0.2 mm/s and thus an upper limit for the beam quality parameter is M ²=2.5. We demonstrate the potential of the long interrogation times available with this atom laser beam by measuring the trap frequency in a single measurement. The small beam width together with the long evolution and interrogation time makes this atom laser beam a promising tool for continuous interferometric measurements.     

Sparse Convex Clustering

Convex clustering, a convex relaxation of k-means clustering and hierarchical clustering, has drawn recent attentions since it nicely addresses the instability issue of traditional nonconvex clustering methods. Although its computational and statistical properties have been recently studied, the performance of convex clustering has not yet been investigated in the high-dimensional clustering scenario, where the data contains a large number of features and many of them carry no information about the clustering structure. In this article, we demonstrate that the performance of convex clustering could be distorted when the uninformative features are included in the clustering. To overcome it, we introduce a new clustering method, referred to as Sparse Convex Clustering, to simultaneously cluster observations and conduct feature selection. The key idea is to formulate convex clustering in a form of regularization, with an adaptive group-lasso penalty term on cluster centers. To optimally balance the trade-off between the cluster fitting and sparsity, a tuning criterion based on clustering stability is developed. Theoretically, we obtain a finite sample error bound for our estimator and further establish its variable selection consistency. The effectiveness of the proposed method is examined through a variety of numerical experiments and a real data application. Supplementary material for this article is available online.     

A curve of nilpotent Lie algebras which are not Einstein nilradicals

The only known examples of non-compact Einstein homogeneous spaces are standard solvmanifolds (special solvable Lie groups endowed with a left invariant metric), and according to a long standing conjecture, they might be all. The classification of Einstein solvmanifolds is equivalent to the one of Einstein nilradicals, i.e. nilpotent Lie algebras which are nilradicals of the Lie algebras of Einstein solvmanifolds. Up to now, very few examples of \mathbb N{\mathbb N}-graded nilpotent Lie algebras that cannot be Einstein nilradicals have been found. In particular, in each dimension, there are only finitely many known. We exhibit in the present paper two curves of pairwise non-isomorphic nine-dimensional two-step nilpotent Lie algebras which are not Einstein nilradicals.     

Two-dimensional crystal growth and stacking of bis(phthalocyaninato) rare earth sandwich complexes at the 1-phenyloctane/graphite interface

Initial stages of two-dimensional crystal growth of the double-decker sandwich complex Lu(Pc*)2 [Pc* = 2,3,9,10,16,17,23,24-octakis(octyloxy)phthalocyaninato] have been studied by scanning tunneling microscopy at the liquid/solid interface between 1-phenyloctane and highly oriented pyrolytic graphite. High-resolution images strongly suggest alignment of the double-decker molecules into monolayers with the phthalocyanine rings parallel to the surface. Domains were observed with either hexagonal or quadrate packing motifs, and the growing interface of the layer was imaged. Molecular resolution was achieved, and the face of the phthalocyanine rings appeared as somewhat diffuse circular features. The alkyl chains are proposed to be interdigitating to maintain planar side-by-side packing.     

Polymer‐free,low tension graphene mechanical resonators

Graphene resonators are fabricated using a polymer‐free, direct transfer method onto metal reinforced holey carbon grids. The resonators are distinguished by the absence of organic residues and excellent crystallinity. The normal mode frequencies are measured using a Fabry–Perot technique; resonance curves indicate highly linear behaviour but very little built‐in strain, which is consistent with device geometry examined by atomic force microscopy. We conclude that the oscillators' restoring force is due instead to graphene's intrinsic bending rigidity; our measurements indicate a value of approximately 1.0 eV, consistent with previous theoretical and experimental work. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Flexible hiring in a make to order system with parallel processing units

In this paper, we study a make-to-order production system with parallel, identical processing units. Each order needs to be satisfied on a single processing unit that is run by a crew. The inter-arrival time and the service time for each order are random variables. The system operates under a lead time performance constraint, which demands the completion of each order within a pre-determined lead time with a certain probability. The minimum number of processing units needed to satisfy this constraint is determined at the tactical level. Our research focuses on the cost savings that can be realized with the use of flexible crews via contractual hiring agreements with an External Labor Supply Agency (ELSA). The ELSA can periodically provide an agreed number of crews. The cost incurred for a flexible crew is higher than that for a permanent crew, and is decreasing in the period length. We model and analyze this system using the transient behavior analysis of multi-server queues and propose several empirically testable functions for the cost of flexible crews. In our computational study, we demonstrate possible cost savings of 2-level, threshold type hiring policies, relative to the fixed capacity system, under 9 scenarios with three demand-to-processing rate ratios and three lead time performance constraints, each of which reflects a different level of ambition. We observe that the maximum savings occur when the cost of a flexible crew is same as that of a permanent crew, and range from 29.38% to 50.56%. However, as the flexible crews become more expensive, the system may choose to employ permanent crews only. We observe that cost savings consist of two parts: savings due to the cancellation of the sclerosis of capacity discreteness, and savings due to the use of workload information in hiring actions. The latter part is higher for more ambitious lead time performance constraints, and for higher mean processing times. Finally, when there is an additional cost for transacting an agreement with the ELSA, we observe that the capacity flexibility option loses its charm, especially if the transaction cost is higher than the cost of a permanent crew.     

Properties and applications of precision oligomer materials; where organic and polymer chemistry join forces

Precise oligomeric materials constitute a growing area of research with implications for various applications as well as fundamental studies. Notably, this field of science which can be termed macro-organic chemistry, draws inspiration from both traditional polymer chemistry and organic synthesis, combining the molecular precision of organic chemistry with the materials properties of macromolecules. Discrete oligomers enable access to unprecedented materials properties, for example, in self-assembled structures, crystallization, or optical properties. The degree of control over oligomer structures resembles many biological systems and enables the design of materials with tailored properties and the development of fundamental structure–property relationships. This Review highlights recent developments in macro-organic chemistry from synthetic concepts to materials properties, with a focus on self-assembly and molecular recognition. Finally, an outlook for future research directions is provided.