Anomalous temperature dependence of speed of sound of bulk poly(N-isopropylacrylamide) hydrogels near the phase transition

Bulk Poly(N-isopropylacrylamide) (PNIPAm) hydrogels are thermally responsive polymers that undergo a sharp volumetric phase transition around its lower critical solution temperature of 33 °C. The physical characteristics of bulk, micro-, and nano-form PNIPAm hydrogel have been well-studied, and have applications ranging from biomedical devices to mechanical actuators. An important physical characteristics which reveals lack of available information is speed of sound. Prior studies have utilized Brillouin scattering, multi-echo reflection ultrasound spectroscopy, the sing-around method, and others in measuring the speed of sound. We use a planar resonant cavity with bulk PNIPAm hydrogel in aqueous solution to determine the temperature dependent speed of sound around the lower critical solution temperature. The results show sharp nonmonotonic behavior of the sound velocity in vicinity of the phase transition.     

A regioselective 1,3‐dipolar cycloaddition of 2‐arylidene‐1‐tetralones with DPNI

Synthesis of a series of novel 1,3‐diphe nyl‐4‐arylspiropyrazolines[5.2¹]‐1¹‐tetralones has been accomplished in good yield by regioselective 1,3‐dipolar cycloaddition of diphenylnitrilimine with (E)‐2‐arylidene‐1‐tetralones. X‐ray crystal structure analysis of one of the products 4b confirms the structure and the regiochemistry of cycloaddition. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 331–336, 1999     

Dielectrophoretic ultra-high-frequency characterization and in silico sorting on uptake of rare earth elements by Cupriavidus necator

Rare earth elements (REEs) are widely used across different industries due to their exceptional magnetic and electrical properties. In this work, Cupriavidus necator is characterized using dielectrophoretic ultra-high-frequency measurements, typically in MHz range to quantify the properties of cytoplasm in C. necator for its metal uptake/bioaccumulation capacity. Cupriavidus necator, a Gram-negative bacteria strain is exposed to REEs like europium, samarium, and neodymium in this study. Dielectrophoretic crossover frequency experiments were performed on the native C. necator species pre- and post-exposure to the REEs at MHz frequency range. The net conductivity of native C. necator, Cupriavidus europium, Cupriavidus samarium, and Cupriavidus neodymium are 15.95 ± 0.029 μS/cm, 16.15 ± 0.028 μS/cm, 16.05 ± 0.029 μS/cm, 15.61 ± 0.005 μS/cm respectively. The estimated properties of the membrane published by our group are used to develop a microfluidic sorter by modeling and simulation to separate REE absorbed C. necator from the unabsorbed native C. necator species using COMSOL Multiphysics commercial software package v5.5.     

Perturbation Solution for One-Dimensional Flow to a Constant-Pressure Boundary in a Stress-Sensitive Reservoir

Transport in Porous Media - Most analyses of fluid flow in porous media are conducted under the assumption that the permeability is constant. In some “stress-sensitive” rock formations,...     

Electro‐osmotic surface effects generation in an electrokinetic‐based transport device: A comparison of RF and MW plasma generating sources

It is a common practice in insulator‐based dielectrophoretic separation to use and reuse PDMS‐constructed microdevice for an extended period of time while performing biological and technical replicate experiments. This is usually done to rule out any effects of device variation on separation efficiency. Ensuring that all experimental conditions remain the same is critical to the conclusion that can be drawn from such repeated experiments. One important contributing factor to the flow of materials within the device is electro‐osmotic velocity, which stems from the surface condition of the device construction materials. In this paper, we present an affordable microwave‐based (MESA‐Mgen) oxygen plasma cleaner developed for approximately less than $100 using readily obtainable parts from an average local hardware store with no specialized tools. This low‐cost room‐air microwave plasma generator was designed using an R‐4055, 400 W, 2450 MHz half‐pint household microwave oven (Sharp ® ) for exploring the possibility of sealing polydimethylsiloxane (PDMS) devices onto glass with minimal budgetary commitment. Microfluidic channels generated using MESA‐Mgen were evaluated for their electro‐osmotic velocities while factors including contact angles, storage‐solvent, half‐way hydrophobicity period were also explored with MESA‐Mgen, and the results were compared to those obtained from the commercially available plasma cleaner (COM‐PC). These outcomes revealed that the MESA‐Mgen induced hydrophilicity and ensured leak‐free sealing of PDMS substrates in a manner comparable with the COM‐PC.     

Generalized Fourier transforms for the acoustic pressure and velocity in compressible dissipative stratified media

Generalized Fourier transforms are derived for the acoustic pressure and velocity in compressible dissipative plane stratified media. The acoustic source terms are accounted for in the equations of continuity and force. The acoustic pressure and velocity are each expressed as sums of two infinite (branch cut) integrals and a discrete term. In the far field the infinite integrals correspond to the direct and specularly reflected waves and the lateral wave. The discrete term associated with the pole of the reflection coefficient is the surface wave. The transforms provide a suitable basis for the expansion of the acoustic pressure and the velocity when the height of the interface, the adiabatic bulk modulus, the equilibrium density, and the absorption of the medium vary. Both exact boundary conditions and the approximate impedance boundary condition are considered in this work.     

Influence of atomic recoil on power broadened lineshapes in 2-level atoms

The power broadened absorption lineshapes of 2-level sodium atoms were carefully studied, using a frequency stabilized cw dye laser and a highly collimated atomic beam. At low driving fields the absorption lineshape was lorentzian as expected. However, at field intensities greater than 50 mW/cm², the lineshape exhibited an asymmetry which was attributed to atomic recoil effects.     

Precision measurements of hyperfine predissociation in I2 vapor using a two-photon resonant scattering technique

A two-photon resonant scattering technique is used to measure natural linewidths of individual hyperfine components of the ν′ = 43,J′ = 12 and 16 rovibrational levels in the I₂ B state (³π_ou⁺). Differences in the linewidths due to hyperfine predissociation are precisely determined. The predissociation constants and the radiative linewidth for ν′ = 43 are found to be [a_ν′]² = 3.36 ± 0.09 kHz, [c_ν′]² = 4.67 ± 0.51 Hz and Γ_r = 51 ± 4 kHz, respectively.     

Laser-molecular beam measurement of hyperfine structure in the I2 spectrum

Very high resolution measurements of hyperfine structure on the P(13) and R(15), 43?0, $\text{3}{}_{\mathrm{gp}}{}_0{}^{\mathrm{+}}{}_{\mathrm{u}}\text{←}{}^1\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{+}}$ transitions in iodine 127 were made using laser molecular beam spectroscopy. The observed linewidth was 300 kHz (fwhm) giving a resolution of 5 × 10^?10 The observed spectrum was fitted to obtain a quadrupole coupling strength difference of ΔeQq = 1906 ± 2 MHz and a spin rotation interaction strength difference of ΔC_I = 181 ± 7 kHz between the upper and lower levels of the P(13) transition. For the R (15) transition ΔeQq = 1905 ± 2 MHz and ΔC_I = 167 ± 5 kHz.     

Dielectric characterization of Babesia bovis using the dielectrophoretic crossover frequency

Coinfection with the tick-transmitted pathogen Babesia spp. is becoming a serious health problem because of the erythrocyte invasion through Ixodes scapularis tick. The transmission of this protozoan by blood transfusion often results in high morbidity and mortality in recipients. A novel way to detect parasitized erythrocytes is by utilizing dielectrophoresis, an electrokinetic technique on a microfluidic platform, to improve the diagnostics of Babesia spp. The differences in the dielectric properties of Babesia spp.–infected erythrocytes versus healthy erythrocytes were exploited to design a fast and cost-effective diagnostic tool. One crucial factor for a successful diagnostic platform via dielectrophoretic separation is the dielectric characterization of Babesia-infected erythrocytes, which is investigated in this paper. The influence of medium conductivity and erythrocytes phenotype and genotype over the first crossover frequency (f_co1) are used to quantify the dielectric properties of the infected cells. A sigmoidal curve was plotted via curve fitting of the single-shell model, which has been proven appropriate for parasitized cell populations where considerable cell geometry variation occurs. The difference in these curves is relevant for the separation of cells population. Microliters of sample and reagent were used throughout this experiment; the scale, results obtained, and simplicity of the system often make it very suitable for point-of-care babesiosis disease diagnostics.