Aerodynamic Focusing Effect in a Rectangular Slit Real Impactor at Different Reynolds Numbers

Numerical investigations were performed to assess the effect of “aerodynamic focusing” achievable by varying the angle of approach in the convergence section of a rectangular slit real impactor, at different Reynolds numbers. Computational Fluid Dynamics (CFD) approach was used as a tool in the study. Simulations were performed on a slit impactor in which the angle of approach in the inlet section was varied from 15° to 75°, at three different Reynolds number values namely 200, 1000, and 2000, to characterize the effect of “aerodynamic focusing”. It is found from the results of the study that the impactor efficiency curve and cut‐point SQRT (Stk)₅₀ value are strong functions of the above parameters. Aerodynamic focusing effect achievable by varying the angle of inlet convergence section is delineated with appropriate particle tracks. Results of the study are expressed as a surface plot of the cut‐point SQRT (Stk)₅₀ value as a function of the Reynolds number and the angle of approach and a correlation relating the parameters is presented.     

A new salicin derivative from the stem bark of Populus davidiana

Phytochemical study on the BuOH-soluble fraction of the stem bark of Populus davidiana resulted in the isolation of a new salicin derivative(1),named davidianoside.The structure was elucidated on the basis of extensive physicochemical and spectroscopic analyses.     

Three-dimensional NMR microscopy: improving SNR with temperature and microcoils.

It is widely held that the spatial resolution achievable by NMR microscopic imaging is limited in biological systems by diffusion to approximately 1-5 microns. However, these estimates were developed for specific imaging techniques and represent practical rather than fundamental limits. NMR imaging is limited by the signal-to-noise ratio (SNR). Diffusion effects on spatial resolution can be made arbitrarily small in principle by increasing the gradient strength. The exponential signal attenuation from random spin motion in a gradient, however, will reduce the signal far below the noise level when the voxel size is reduced much below 5 microns. Two factors can be optimized to improve the SNR: (1) the inductive linkage between microscopic samples and the detection apparatus and (2) the temperature of the rf probe. In this work, the filling factor was optimized using inductors with diameters less than 1 mm. It is furthermore shown that probe circuit cooling results in significant improvements in SNR, whereas cooling of the preamplifier is of little value when proper noise matching between the resonant circuit and preamplifier is accomplished. Using three-dimensional Fourier imaging techniques, we have obtained images of single-cell organisms with spatial resolution of approximately 6 microns. Practical limitations include mechanical stability of the apparatus, thermal shielding between the sample and probe, and the magnetic susceptibility of the sample.     

Structural studies and T c dependence in La2−x Dy x Ca y Ba2Cu4+y O z type mixed oxide superconductors

A new series of mixed oxide superconductors with the stoichiometric composition La_2−x Dy _x Ca _y Ba₂Cu_4+y O _z (x=0.0 − 0.5, y=2x) has been studied for structural and superconductiong properties. Our earlier studies on La_2−x (Y/Er) _x Ca _y Ba₂Cu_4+y O _z series, show a strong dependence of T _c on hole concentration (p _sh). In the present work, the results of the analysis of the neutron diffraction measurements at room temprerature on x=0.3 and 0.5 samples are reported. It is interesting to know that Ca substitutes for both La and Ba site with concomitant displacement of La onto Ba site. Superconductivity studies show that maximum T _c is obtained for x=0.5, y=1.0 sample (T _c ∼ 75 K), for La_1.5Dy_0.5Ca₁Ba₂Cu₅O _z (La-2125).     

Vocalizations produced by humpback whale (Megaptera novaeangliae) calves recorded in Hawaii

Although humpback whale (Megaptera novaeangliae) calves are reported to vocalize, this has not been measurably verified. During March 2006, an underwater video camera and two-element hydrophone array were used to record nonsong vocalizations from a mother-calf escort off Hawaii. Acoustic data were analyzed; measured time delays between hydrophones provided bearings to 21 distinct vocalizations produced by the male calf. Signals were pulsed (71%), frequency modulated (19%), or amplitude modulated (10%). They were of simple structure, low frequency (mean=220 Hz), brief duration (mean=170 ms), and relatively narrow bandwidth (mean=2 kHz). The calf produced three series of "grunts" when approaching the diver. During winters of the years 2001-2005 in Hawaii, nonsong vocalizations were recorded in 109 (65%) of 169 groups with a calf using an underwater video and single (omnidirectional) hydrophone. Nonsong vocalizations were most common (34 of 39) in lone mother-calf pairs. A subsample from this dataset of 60 signals assessed to be vocalizations provided strong evidence that 10 male and 18 female calves vocalized based on statistical similarity to the 21 verified calf signals, proximity to an isolated calf (27 of 28 calves), strong signal-to-noise ratio, and/or bubble emissions coincident to sound.     

A micromechanical mass sensing method based on amplitude tracking within an ultra-wide broadband resonance

We propose a mass sensing scheme in which amplitude shifts within a nonlinear ultra-wide broadband resonance serve as indicators for mass detection. To achieve the broad resonance bandwidth, we considered a nonlinear design of the resonator comprised of a doubly clamped beam with a concentrated mass at its center. A reduced-order model of the beam system was constructed in the form of a discrete spring-mass system that contains cubic stiffness due to axial stretching of the beam in addition to linear stiffness (Duffing equation). The cubic nonlinearity has a stiffening effect on the frequency response causing nonlinear bending of the frequency response toward higher frequencies. Interestingly, we found that the presence of the concentrated mass broadens the resonant bandwidth significantly, allowing for an ultra-wide operational range of frequencies and response amplitudes in the proposed mass sensing scheme. A secondary effect of the cubic nonlinearity is strong amplification of the third harmonic in the beam’s response. We computationally study the sensitivity of the first and third harmonic amplitudes to mass addition and find that both metrics are more sensitive than the linearized natural frequency and that in particular, the third harmonic amplitude is most sensitive. This type of open-loop mass sensing avoids complex feedback control and time-consuming frequency sweeping. Moreover, the mass resolution is within a functional range, and the design parameters of the resonator are reasonable from a manufacturing perspective.     

Direct propylene epoxidation on chemically reduced Au nanoparticles supported on titania

A highly selective titania supported propylene epoxidation catalyst was synthesized from chemically reduced, thiol capped, gold nanoparticles, and characterized by TEM and XPS.     

Correlation of urokinase activity from biopotency and high-performance liquid chromatographic assays

A simpler, less expensive, and faster high-performance liquid chromatographic method was shown to be an alternative to urokinase potency determinations by the Ploug method. Post-elution recovery of the low-molecular-weight form was 104 +/- 2.4% as determined by the Ploug method. Two analysts reported relative standard deviations of 1.6% and 1.1% based on peak height determination of eight replicate injections of a single sample of low-molecular-weight material. Linearity at the same wavelength for low- and high-molecular-weight forms was 0.9999 and 0.9992, respectively, for peak height versus potency.