Fabrication and performance of a microfluidic traveling-wave electrophoresis system

A microfluidic traveling-wave electrophoresis (TWE) system is reported that uses a locally defined traveling electric field wave within a microfluidic channel to achieve band transport and separation. Low voltages, over a range of -0.5 to +0.5 V, are used to avoid electrolysis and other detrimental redox reactions while the short distance between electrodes, ～25 μm, provides high electric fields of ～200 V cm(-1). It is expected that the low voltage requirements will simplify the future development of smaller portable devices. The TWE device uses four interdigitated electrode arrays: one interdigitated electrode array pair is on the top of the microchannel and the other interdigitated electrode array pair is on the microchannel bottom. The top and bottom substrates are joined by a PDMS spacer that has a nominal height of 15 μm. A pinched injection scheme is used to define a narrow sample band within an injection cross either electrokinetically or hydrodynamically. Separation of two dyes, fluorescein and FLCA, with baseline resolution is achieved in less than 3 min and separation of two proteins, insulin and casein is demonstrated. Investigation of band broadening with fluorescein reveals that sample band widths equivalent to the diffusion limit can be achieved within the microfluidic channel, yielding highly efficient separations. This low level of band broadening can be achieved with capillary electrophoresis, but is not routinely observed in microchannel electrophoresis. Sample enrichment can be achieved very easily with TWE using a device with converging electric field waves controlled by two sets of independently controlled interdigitated electrodes arrays positioned serially along the microchannel. Sample enrichment of 40-fold is achieved without heterogeneous buffer/solvent systems, sorptive, or permselective materials. While there is much room for improvement in device fabrication, and many capabilities are yet to be demonstrated, it is anticipated that the capabilities and performance demonstrated herein will enable new lab-on-a-chip processes and systems.     

Synthesis and Crystal Structure of Cs(VO2)3(TeO3)2, a New Layered Cesium Vanadium(V) Tellurite

Synthetic Cs(VO₂)₃(TeO₃)₂ is built up from infinite sheets of distorted octahedral V^VO₆ groups, sharing vertices. These octahedral layers are “capped” by Te atoms (as parts of pyramidal [Te^IVO₃]^2– groups) on both faces of each V/O sheet, with inter‐layer, 12‐coordinate, Cs⁺ cations providing charge compensation. Cs(VO₂)₃(TeO₃)₂ is isostructural with M(VO₂)₃(SeO₃)₂ (M = NH₄, K). Crystal data: Cs(VO₂)₃(TeO₃)₂, M_r = 732.93, hexagonal, space group P6₃ (No. 173), a = 7.2351(9) Å, c = 11.584(2) Å, V = 525.1(2) ų, Z = 2, R(F) = 0.030, wR(F ²) = 0.063.     

Nanostructures versus solid solutions: low lattice thermal conductivity and enhanced thermoelectric figure of merit in Pb9.6Sb0.2Te10-xSex bulk materials

The series of Pb(9.6)Sb(0.2)Te(10)(-)(x)Se(x) compounds with different Se content (x) were prepared, and their structure was investigated at the atomic and nanosized regime level. Thermoelectric properties were measured in the temperature range from 300 to 700 K. The Pb(9.6)Sb(0.2)Te(10)(-)(x)Se(x) series was designed after the refinement of the single-crystal structure of Pb(3.82)Sb(0.12)Te(4) (Pb(9.6)Sb(0.3)Te(10); S.G. Pmm) by substituting isoelectronically in anion positions Te by Se. The Pb(9.6)Sb(0.2)Te(10)(-)(x)Se(x)() compounds show significantly lower lattice thermal conductivity (kappa(L)) compared to the well-known PbTe(1)(-)(x)Se(x) solid solutions. For Pb(9.6)Sb(0.2)Te(3)Se(7) (x = 7), a kappa(L) value as low as 0.40 W/m.K was determined at 700 K. High-resolution transmission electron microscopy of several Pb(9.6)Sb(0.2)Te(10)(-)(x)Se(x) samples showed widely distributed Sb-rich nanocrystals in the samples which is the key feature for the strong reduction of the lattice thermal conductivity. The reduction of kappa(L) results in a significantly enhanced thermoelectric figure of merit of Pb(9.6)Sb(0.2)Te(10)(-)(x)Se(x) compared to the corresponding PbTe(1)(-)(x)Se(x) solid solution alloys. For Pb(9.6)Sb(0.2)Te(3)Se(7) (x = 7), a maximum figure of merit of ZT approximately 1.2 was obtained at approximately 650 K. This value is about 50% higher than that of the state-of-the-art n-type PbTe. The work provides experimental validation of the theoretical concept that embedded nanocrystals can promote strong scattering of acoustic phonons.     

Fonctions méromorphes aux zéros et pôles communs

Hinkkanen's problem (1984) is completely solved, i.e., it is shown that any meromorphic function f of one complex variable is determined by its zeros and poles and the zeros of f^(j) for j=1,2,3,4. To cite this article: G. Frank et al., C. R. Acad. Sci. Paris, Ser. I 338 (2004).     

Crowdsourcing Natural Products Discovery to Access Uncharted Dimensions of Fungal Metabolite Diversity

A fundamental component for success in drug discovery is the ability to assemble and screen compounds that encompass a broad swath of biologically relevant chemical‐diversity space. Achieving this goal in a natural‐products‐based setting requires access to a wide range of biologically diverse specimens. For this reason, we introduced a crowdsourcing program in which citizen scientists furnish soil samples from which new microbial isolates are procured. Illustrating the strength of this approach, we obtained a unique fungal metabolite, maximiscin, from a crowdsourced Alaskan soil sample. Maximiscin, which exhibits a putative combination of polyketide synthase (PKS), non‐ribosomal peptide synthetase (NRPS), and shikimate pathway components, was identified as an inhibitor of UACC‐62 melanoma cells (LC50=0.93 μM ). The metabolite also exhibited efficacy in a xenograft mouse model. These results underscore the value of building cooperative relationships between research teams and citizen scientists to enrich drug discovery efforts.     

Identification of auditory distance cues by zebra finches (Taeniopygia guttata) and budgerigars (Melopsittacus undulatus)

The present study examined auditory distance perception cues in a non-territorial songbird, the zebra finch (Taeniopygia guttata), and in a non-songbird, the budgerigar (Melopsittacus undulatus). Using operant conditioning procedures, three zebra finches and three budgerigars were trained to identify 1- (Near) and 75-m (Far) recordings of three budgerigar contact calls, one male zebra finch song, and one female zebra finch call. Once the birds were trained on these endpoint stimuli, other stimuli were introduced into the operant task. These stimuli included recordings at intermediate distances and artificially altered stimuli simulating changes in overall amplitude, high-frequency attenuation, reverberation, and all three cues combined. By examining distance cues (amplitude, high-frequency attenuation, and reverberation) separately, this study sought to determine which cue was the most salient for the birds. The results suggest that both species could scale the stimuli on a continuum from Near to Far and that amplitude was the most important cue for these birds in auditory distance perception, as in humans and other animals.     

One-step 9-stage Hermite–Birkhoff–Taylor ODE solver of order 10

A one-step 9-stage Hermite–Birkhoff–Taylor method of order 10, denoted by HBT(10)9, is constructed for solving nonstiff systems of first-order differential equations of the form y′=f(x,y), y(x ₀)=y ₀. The method uses y′ and higher derivatives y ⁽²⁾ to y ⁽⁴⁾ as in Taylor methods and is combined with a 9-stage Runge–Kutta method. Forcing a Taylor expansion of the numerical solution to agree with an expansion of the true solution leads to Taylor- and Runge–Kutta-type order conditions which are reorganized into Vandermonde-type linear systems whose solutions are the coefficients of the method. The new method has a larger scaled interval of absolute stability than Dormand–Prince DP(8,7)13M. The stepsize is controlled by means of y ⁽²⁾ and y ⁽⁴⁾. HBT(10)9 is superior to DP(8,7)13M and Taylor method of order 10 in solving several problems often used to test high-order ODE solvers on the basis of the number of steps, CPU time, and maximum global error. These numerical results show the benefits of adding high-order derivatives to Runge–Kutta methods.