Relative periodic orbits in plane Poiseuille flow

A branch of relative periodic orbits is found in plane Poiseuille flow in a periodic domain at Reynolds numbers ranging from Re=3000$\mathit{Re}=3000$ to Re=5000$\mathit{Re}=5000$. These solutions consist in sinuous quasi-streamwise streaks periodically forced by quasi-streamwise vortices in a self-sustained process. The streaks and the vortices are located in the bulk of the flow. Only the amplitude, but not the shape, of the averaged velocity components does change as the Reynolds number is increased from 3000 to 5000. We conjecture that these solutions could therefore be related to large- and very large-scale structures observed in the bulk of fully developed turbulent channel flows.     

Implementing compressive fractional Fourier transformation with iterative kernel steering regression in double random phase encoding

This paper proposes a novel approach in double random phase encryption based on compressive fractional Fourier transform along with the kernel steering regression. The method increases the complexity of the image by using fractional Fourier transform and taking fewer measurements from the image data. Numerical results are given to analyze the validity of this technique. Considering natural images to be sparse in some domain, we apply a compressive sensing (CS) approach by using a TwIST algorithm. The encryption process has kernel steering regression algorithm for denoising and compressive sensing technique for image compression along with the fractional Fourier transform that makes the image in more complex form.     

First Dual Responsive “Turn-On” and “Ratiometric” AIEgen Probe for Selective Detection of Hydrazine Both in Solution and the Vapour Phase

A new dual responsive “turn-on” and “ratiometric” aggregation-induced emission luminogen (AIEgen) 3-formyl-5-(piperidin-1-yl)biphenyl-4-carbonitrile 6 a (FPBC 6 a ) for selective detection of hydrazine in solution as well as in vapour phase is described. At a low concentration of 2.5 μm , the probe FPBC 6 a is non-fluorescent (turn-off) but remarkably lights up (turn-on with blue emission) in the presence of hydrazine solution (0.25–25 μm ). Interestingly, at higher concentrations, the nanoaggregates of FPBC 6 a (>25 μm , 99 % HEPES in DMSO) displayed ratiometric response in the presence of hydrazine with a remarkable hypsochromic shift from the green (500–550 nm) to blue regions (440–480 nm). Furthermore, a real application of FPBC 6 a was successfully demonstrated through the detection and visualization of hydrazine in live cervical cancer cells as well as using portable test strips.     

Carbonation study and determination of cement to sand ratio in hardened cement mortar by X-ray photoelectron spectroscopy

The determination of cement and sand content in an aged cement mortar is a challenging problem for civil engineers. Techniques like x-ray diffraction (XRD), thermogravimetric analysis (TGA) and electrochemical impedance spectroscopy (EIS) are well established, which can give some insight of the hydrated products. The present study is an attempt to use x-ray photoelectron spectroscopy (XPS) technique for the evaluation of ordinary Portland cement (OPC), sand (aggregate) composition and carbonation study in hardened cement mortar. Carbonation analysis and cement to sand ratio for all mortar compositions has been determined and studied in detail in the present work. The C 1s spectra of cement mortar with ratios 1:1, 1:3 and 1:6 shows carbonate formation on the surface with 21, 40 and 32 atomic percent, respectively. An increase in SiO₂ content corresponding to sand is observed for all three mortar mix. The formation of silica gel due to carbonation has not been observed in the mortar samples. The cement to sand ratio for all three mortar mixes is found to be in 20–30 percent error limit due to the heterogeneous nature of the mortar system.     

Gindarudine,a novel morphine alkaloid from Stephania glabra

A novel morphine alkaloid,named gindarudine 1 has been isolated from ethanol extract of Stephania glabra tubers,together with four known alkaloids,palmatine,dehydrocorydalmine,stepharamne,and 8-(4'-methoxybenzyl)-xylopinine.Compound 1 was elucidated as 3,6-O,N-detrimethyl-10-hydroxy-1-methoxy-thebaine by means of spectroscopic data including 2D NMR studies.     

ZnSe core and ZnSe@ZnS core-shell quantum dots as platform for folic acid sensing

This report demonstrates a quantum dot (QD)-based selective and fast sensor platform for detection of folic acid (FA). This electrochemical platform provides a good linear relation between the anodic and cathodic peak currents (i _pa and i _pc ) in the FA concentration range of 12 to 96 nM, and the minimum detection limit (MDL) achieved was 10 nM. As an extension, absorbance and fluorescence methods were also used for the detection of FA in solutions. Core-shell QDs provided better binding than core-only ZnSe quantum dots, and showed twofold increment in binding constant. A detailed comparative evaluation of the three methods (absorbance, fluorescence, and electrochemical) is presented vis-a-vis real samples. Therefore, in principle absorbance and fluorescence spectroscopy can also be used for detecting folic acid with high selectivity and sensitivity. The MDL can be extended to be 4–7 nM level by using fluorescence and absorbance spectroscopy. FA metabolism occurs in the intestine, where the pH conditions are basic. Hence, sensing of FA under physiological conditions is relevant, which was achieved in our case. Earlier methods have reported sensing under acidic or neutral pH conditions. Considering the importance of folic acid in physiology, the significance of the present study can be hardly stressed.

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Graphical abstract Interaction of ZnSe and ZnSe@ZnS QDs with Folic acid

     

Self-organized nanostructure formation on the graphite surface induced by helium ion irradiation

The effects of helium ion irradiation on the graphite surface are studied by employing a plasma focus device. The device emits helium ion pulse having energies in the range of a few keV to a few MeV and flux on the order of 10²⁵ m^?2?s^?1 at 60 mm axial position from the anode tip. The field emission scanning electron microscopy confirms the formation of multi-modal spherical and elongated agglomerated structures on irradiated samples surface with increase in agglomerate size with increasing number of irradiation shots. The transient annealing in each irradiation was not enough to cause the Oswald ripening or sintering of particles into bigger particle or crystal size but only resulted in clustering. The atomic force micrographs reveal an increase in average surface roughness with increasing ion irradiation. The Raman study demonstrates increase in disordered D peak along with reduced crystallite size ($L_a$) with increasing number of irradiation shots.     

Effect of Zeeman Slower Beam on Loading of a Krypton Magneto-Optical Trap

We report the studies on the effect of Zeeman slower beam power on the loading rate and collision loss rate in an atomic beam loaded krypton magneto-optical trap (MOT). The results show that an increase in Zeeman slower beam power initially increases the MOT loading rate and reduces the background collision loss rate to increase the number of cold atoms in the MOT to an optimum value. With further increase in the Zeeman slower beam power, the number of cold atoms in the MOT decreases due to increased background collision loss rate and decrease in the trap loading rate. However, the cold collision loss rate is observed to remain unaffected by the variation in the Zeeman slower beam power. Therefore, the study emphasizes the need to optimize the Zeeman slower beam power to trap maximum number of cold atoms in an atomic beam loaded MOT.     

Magnetic force microscopic study of the magnetic field induced antiferro to ferrimagnetic transition in Mn1.85Co0.15Sb

Magnetic field induced first order antiferromagnetic (AFM) to ferrimagnetic (FRI) transition in polycrystalline Mn_1.85Co_0.15Sb has been studied using magnetic force microscopy (MFM) at 60 K and up to 8 T magnetic fields. Our MFM studies provide real space visualization of AFM to FRI transition. It shows growth (decay) of FRI phase with increasing (decreasing) magnetic field. The hysteretic behavior and co-existing FRI and AFM phases across the critical field required for FRI-AFM transition in Mn_1.85Co_0.15Sb are highlighted. This study demonstrates the potential of MFM for studying phase co-existence at high field and low temperatures.     

Self-organized transformation to polyaniline nanowires by pulsed energetic electron irradiation in a plasma focus device

An ingenious method for fabricating network of polyaniline nanowires at room temperature in microsecond timescale is demonstrated by using the pulsed electron beam of a plasma focus device. The electron beam of the plasma focus device having a wide range of energies (10-200 keV) was irradiated on to the freestanding polyaniline film. The growth of polyaniline nanowires on the surface of film sample is confirmed by field emission scanning electron microscope images showing nanowires of about 50-80 nm in diameter and up to few tens of micrometers in length.