Accessing Ambiphilic Phosphine Boronates through C−H Borylation by an Unforeseen Cationic Iridium Complex

Ambiphilic molecules, which contain a Lewis base and Lewis acid, are of great interest based on their unique ability to activate small molecules. Phosphine boronates are one class of these substrates that have interesting catalytic activity. Direct access to these phosphine boronates is described through the iridium‐catalyzed C?H borylation of phosphines. An unconventional cationic iridium catalyst was identified as optimal for a range of phosphines, providing good yields and selectivity across a diverse class of phosphine boronates (isolated as the borane‐protected phosphine). A complimentary catalyst system (quinoline‐based silane ligand with [(COD)IrOMe]₂) was optimal for biphenyl‐based phosphines. Selective polyborylation was also shown providing bis‐ and tris‐borylated phosphines. Deprotection of the phosphine boronate provided free ambiphilic phosphine boronates, which do not have detectable interactions between the phosphorus and boron atoms in solution or the solid state.     

The Busy Period of the M/GI/∞ Queue

An equation for the distribution Z() of the duration T of the busy period in a stationary M/GI/ service system is constructed from first principles. Two scenarios are examined, being distinguished by the half-plane Re()>₀ for some ₀0 in which the generic service time random variable S, always assumed to have a finite mean E(S), has an analytic Laplace–Stieltjes transform E(e^–S ). If ₀<0 then E(e^–T ) is analytic in a half-plane (₁,), where ₀₁<0 and ₁ is determined by the distribution of S; then for any 0<s<|₁|.When ₀=0, E(e^–T ) is analytic in (0,), and now more is known about T. Inequalities on the tail () are used to show that for any 1, E(T ) is finite if and only if E(S ) is finite. It follows that the point process consisting of the starting epochs of busy periods is long range dependent if and only if E(S ²)=, in which case it has Hurst index equal to [frac12](3–), where is the moment index of S.If also the tail (x)=Pr{Sx} of the service time distribution satisfies the subexponential density condition ₀ ^x (x–u) (u)du/ (x)2E(S) as x, then (x)/ (x)e^E(S), where is the arrival rate.     

Defect-suppressed atomic crystals in an optical lattice

We present a coherent filtering scheme which dramatically reduces the site occupation number defects for atoms in an optical lattice by transferring a chosen number of atoms to a different internal state via adiabatic passage. With the addition of superlattices it is possible to engineer states with a specific number of atoms per site (atomic crystals), which are required for quantum computation and the realization of models from condensed matter physics, including doping and spatial patterns. The same techniques can be used to measure two-body spatial correlation functions.     

Single atom transistor in a 1D optical lattice

We propose a scheme utilizing a quantum interference phenomenon to switch the transport of atoms in a 1D optical lattice through a site containing an impurity atom. The impurity represents a qubit which in one spin state is transparent to the probe atoms, but in the other acts as a single atom mirror. This allows a single-shot quantum nondemolition measurement of the qubit spin.     

Viscoelastic locally resonant double negative metamaterials with controllable effective density and elasticity

A metamaterial that is composed of solid viscoelastic elements with controllable properties is proposed in this Letter. This enables an adaptable and general acoustic metamaterial to be practically realised. An array of masses with a single elastic connection to a supporting viscoelastic structure, such as one that is dynamically equivalent to an array of Helmholtz resonators, only provides a system with negative effective mass. A local active control scheme applied to each of these masses can emulate additional elastic connections to the supporting structure. An array of masses with a suitable local control scheme can provide both the negative effective stiffness and mass required for negative refraction. The tuneable feedback control parameters determine the characteristics of the region of double negativity.     

A test of the binaural equal-loudness-ratio hypothesis for tones

It is well known that a tone presented binaurally is louder than the same tone presented monaurally. It is less clear how this loudness ratio changes as a function of level. The present experiment was designed to directly test the Binaural Equal-Loudness-Ratio hypothesis (BELRH), which states that the loudness ratio between equal-SPL monaural and binaural tones is independent of SPL. If true, the BELRH implies that monaural and binaural loudness functions are parallel when plotted on a log scale. Cross-modality matches between string length and loudness were used to directly measure binaural and monaural loudness functions for nine normal listeners. Stimuli were 1-kHz 200-ms tones ranging in level from 5 dB SL to 100 dB SPL. A two-way ANOVA showed significant effects of level and mode (binaural or monaural) on loudness, but no interaction between the level and mode. Consequently, no significant variations were found in the binaural-to-monaural loudness ratio across the range of levels tested. This finding supports the BELRH. In addition, the present data were found to closely match loudness functions derived from binaural level differences for equal loudness using the model proposed by Whilby et al. [J. Acoust. Soc. Am. 119, 3931-3939 (2006)].     

Parallel, fluorous open-tubular chromatography using microstructured fibers

Although commonly used in gas chromatography, open-tubular columns for liquid chromatography have seen their development hindered by a number of factors both theoretical and practical. Requiring small diameters, great lengths and specialized detection systems to achieve a proper chromatographic response, columns of this sort have largely been ignored despite the highly desirable column performance an optimized system would provide. Here, we introduce the use of microstructured fibers (MSFs) as a platform for the development of multiplexed open-tubular liquid chromatography (OTLC) columns. The multiple, parallel silica channels presented by the MSF act as a promising substrate for an OTLC column, as they have diameters near the ideal range for interactions (1–3 μm), minimize flow-induced backpressure through their many uniform paths, and increase the loading capacity compared to a single capillary channel of similar size. Additionally, with outer diameters comparable to regular fused silica capillaries, MSFs can easily be employed in conventional chromatographic systems, eliminating the need for specialized equipment. Finally, MSF columns of this type can be functionalized using silane coupling techniques to allow the introduction of a wide variety of stationary phase chemistries. While in this report we explore the potential and limitations of fluorine-functionalized MSFs as OTLC columns, other stationary phase materials could easily be substituted by choosing appropriate silanization reagents. Particular attention here will be paid to the physical and performance characteristics of the fabricated columns, as well as avenues for their improvement and implementation.     

State-dependent lattices for quantum computing with alkaline-earth-metal atoms

Recent experimental progress with Alkaline-Earth atoms has opened the door to quantum computing schemes in which qubits are encoded in long-lived nuclear spin states, and the metastable electronic states of these species are used for manipulation and readout of the qubits. Here we discuss a variant of these schemes, in which gate operations are performed in nuclear-spin-dependent optical lattices, formed by near-resonant coupling to the metastable excited state. This provides an alternative to a previous scheme [Phys. Rev. Lett. 101, 170504 (2008)], which involved independent lattices for different electronic states. As in the previous case, we show how existing ideas for quantum computing with Alkali atoms such as entanglement via controlled collisions can be freed from important technical restrictions. We also provide additional details on the use of collisional losses from metastable states to perform gate operations via a lossy blockade mechanism.