Molecular probe dynamics reveals suppression of ice-like regions in strongly confined supercooled water

The structure of the hydrogen bond network is a key element for understanding water's thermodynamic and kinetic anomalies. While ambient water is strongly believed to be a uniform, continuous hydrogen-bonded liquid, there is growing consensus that supercooled water is better described in terms of distinct domains with either a low-density ice-like structure or a high-density disordered one. We evidenced two distinct rotational mobilities of probe molecules in interstitial supercooled water of polycrystalline ice Banerjee D, et al. (2009) ESR evidence for 2 coexisting liquid phases in deeply supercooled bulk water. Proc Natl Acad Sci USA 106: 11448-11453]. Here we show that, by increasing the confinement of interstitial water, the mobility of probe molecules, surprisingly, increases. We argue that loose confinement allows the presence of ice-like regions in supercooled water, whereas a tighter confinement yields the suppression of this ordered fraction and leads to higher fluidity. Compelling evidence of the presence of ice-like regions is provided by the probe orientational entropy barrier which is set, through hydrogen bonding, by the configuration of the surrounding water molecules and yields a direct measure of the configurational entropy of the same. We find that, under loose confinement of supercooled water, the entropy barrier surmounted by the slower probe fraction exceeds that of equilibrium water by the melting entropy of ice, whereas no increase of the barrier is observed under stronger confinement. The lower limit of metastability of supercooled water is discussed.

A Chemodosimetric Probe Based on a Conjugated Oxidized Bis-Indolyl System for Selective Naked-Eye Sensing of Cyanide Ions in Water

A new bis-indolyl-based colorimetric probe has been synthesized. This allows a Michael-type adduct formation for the detection of cyanide ions. The probe shows a remarkable color change from red to colorless upon addition of the cyanide ions in pure water. The cyanide ion reacts with the probe and removes the conjugation of the bis-indolyl moiety of the probe with that of the 4-substituted aromatic ring. This renders the probe colorless. The mechanism of the reaction of the probe with the cyanide ion was established by using 1H and 13C NMR spectroscopy, mass spectrometry, and kinetic studies.

Azimuthal Angle Probe of Anomalous HWW Couplings at a High Energy ep Collider

A high energy ep collider, such as the proposed LHeC, possesses the unique facility of permitting direct measurement of the HWW coupling without contamination from the HZZ coupling. At such a machine, the fusion of two W bosons through the HWW vertex would give rise to typical charged current events accompanied by a Higgs boson. We demonstrate that azimuthal angle correlations between the observable charged current final states could then be a sensitive probe of the nature of the HWW vertex and hence of the CP properties of the Higgs boson. DOI: 10.1103/PhysRevLett.109.261801

Ratiometric, reversible, and parts per billion level detection of multiple toxic transition metal ions using a single probe in micellar media

We present the selective sensing of multiple transition metal ions in water using a synthetic single probe. The probe is made up of pyrene and pyridine as signaling and interacting moiety, respectively. The sensor showed different responses toward metal ions just by varying the medium of detection. In organic solvent (acetonitrile), the probe showed selective detection of Hg2+ ion. In water, the fluorescence quenching was observed with three metal ions, Cu2+, Hg2+, and Ni2+. Further, just by varying the surface charge on the micellar aggregates, the probe could detect and discriminate the above-mentioned three different toxic metal ions appropriately. In neutral micelles (Brij 58), the probe showed a selective interaction with Hg2+ ion as observed in acetonitrile medium. However, in anionic micellar medium (sodium dodecyl sulfate, SDS), the probe showed changes with both Cu2+ and Ni2+. under UV-vis absorption spectroscopy. The discrimination between these two ions was achieved by recording their emission spectra, where it showed selective quenching with Cu2+.

Two-axis force sensing and control of a Reorientable scanning probe

This paper presents the design and implementation of a reorientable scanning probe that is capable of two-axis force sensing and control in the 2-D scanning (X-Z) plane. The probe is comprised of three major components, namely a compliant manipulator, laser measurement system, and magnetic actuation system. Control of the position and orientation of the probe tip is realized by means of magnetic actuation combined with a novel structural design. The design of the manipulator's compliance and that of the optical path of the laser measurement system together enable achieving sensitivity to lateral (X) forces that is nearly identical to that of normal (Z) forces. The achieved sensitivity ratio, of about 0.6, is significantly higher than that of conventional scanning probe systems. The theoretical bases for the structural design and the sensitivity of the two-axis force sensing system are presented. Subsequently, fabrication of the manipulator is described and the result of experimental evaluation of the scanning probe's features is discussed. The scanning probe is used to access the vertical and re-entrant features on the two sides of a cylindrical micropipette, which are subsequently scanned by regulating the lateral force of tip-sample interaction.

Analysis of grating inscribed micro-cantilever for high resolution AFM probe

We present a mathematical modelling and analysis of reflection grating etched Si AFM cantilever deflections under different loading conditions. A simple analysis of the effect of grating structures on cantilever deflection is carried out with emphasis on optimizing the beam and gratings such that maximum amount of diffracted light remains within the detector area.

Correspondence between neutron depolarization and higher order magnetic susceptibility to investigate ferromagnetic clusters in phase separated systems

It is a tough task to distinguish a short-range ferromagnetically correlated cluster-glass phase from a canonical spin-glass-like phase in many magnetic oxide systems using conventional magnetometry measurements. As a case study, we investigate the magnetic ground state of La0.85Sr0.15CoO3, which is often debated based on phase separation issues. We report the results of two samples of La0.85Sr0.15CoO3 (S-1 and S-2) prepared under different conditions. Neutron depolarization, higher harmonic ac susceptibility and magnetic relaxation studies were carried out along with conventional magnetometry measurements to differentiate subtle changes at the microscopic level. There is no evidence of ferromagnetic correlation in the sample S-2 attributed to a spin-glass phase, and this is compounded by the lack of existence of a second order component of higher harmonic ac susceptibility and neutron depolarization. A magnetic relaxation experiment at different temperatures complements the spin glass characteristic in S-2. All these signal a sharp variance when we consider the cluster-glass-like phase (phase separated) in S-1, especially when prepared from an improper chemical synthesis process. This shows that the nonlinear ac susceptibility is a viable tool to detect ferromagnetic clusters such as those the neutron depolarization study can reveal.

Small-Angle Neutron Scattering Studies of Hemoglobin Confined Inside Silica Tubes of Varying Sizes

In addition to the chemical nature of the surface, the dimensions of the confining host exert a significant influence on confined protein structures; this results in immense biological implications, especially those concerning the enzymatic activities of the protein. This study probes the structure of hemoglobin (Hb), a model protein, confined inside silica tubes with pore diameters that vary by one order of magnitude (approximate to 20-200 nm). The effect of confinement on the protein structure is probed by comparison with the structure of the protein in solution. Small-angle neutron scattering (SANS), which provides information on protein tertiary and quaternary structures, is employed to study the influence of the tube pore diameter on the structure and configuration of the confined protein in detail. Confinement significantly influences the structural stability of Hb and the structure depends on the Si-tube pore diameter. The high radius of gyration (R-g) and polydispersity of Hb in the 20 nm diameter Si-tube indicates that Hb undergoes a significant amount of aggregation. However, for Si-tube diameters greater or equal to 100 nm, the R-g of Hb is found to be in very close proximity to that obtained from the protein data bank (PDB) reported structure (R-g of native Hb=23.8 angstrom). This strongly indicates that the protein has a preference for the more native-like non-aggregated state if confined inside tubes of diameter greater or equal to 100 nm. Further insight into the Hb structure is obtained from the distance distribution function, p(r), and ab initio models calculated from the SANS patterns. These also suggest that the Si-tube size is a key parameter for protein stability and structure.

An Efficient Probe for Rapid Detection of Cyanide in Water at Parts per Billion Levels and Naked-Eye Detection of Endogenous Cyanide

A new molecular probe based on an oxidized bis-indolyl skeleton has been developed for rapid and sensitive visual detection of cyanide ions in water and also for the detection of endogenously bound cyanide. The probe allows the naked-eye detection of cyanide ions in water with a visual color change from red to yellow ((max)=80nm) with the immediate addition of the probe. It shows high selectivity towards the cyanide ion without any interference from other anions. The detection of cyanide by the probe is ratiometric, thus making the detection quantitative. A Michael-type addition reaction of the probe with the cyanide ion takes place during this chemodosimetric process. In water, the detection limit was found to be at the parts per million level, which improved drastically when a neutral micellar medium was employed, and it showed a parts-per-billion-level detection, which is even 25-fold lower than the permitted limits of cyanide in water. The probe could also efficiently detect the endogenously bound cyanide in cassava (a staple food) with a clear visual color change without requiring any sample pretreatment and/or any special reaction conditions such as pH or temperature. Thus the probe could serve as a practical naked-eye probe for in-field experiments without requiring any sophisticated instruments.

Universal Conductance Fluctuations as a direct probe to valley coherence and universality class of disordered graphene

We demonstrate that the universal conductance fluctuations (UCF) can be used as a direct probe to study the valley quantum states in disordered graphene. The UCF magnitude in graphene is suppressed by a factor of four at high carrier densities where the short-range disorder essentially breaks the valley degeneracy of the K and K' valleys, leading to a density dependent crossover of symmetry class from symplectic near the Dirac point to orthogonal at high densities.

Revised density of magnetized nuclear matter at the neutron drip line

We study the onset of the neutron drip in high-density matter in the presence of a magnetic field. It has been found that, for systems having only protons and electrons, in the presence of a magnetic field greater than or similar to 10(15) G, neutronization occurs at a density that is at least an order of magnitude higher compared to that in a nonmagnetic system. In a system with heavier ions, the effect of the magnetic field, however, starts arising at a much higher field, greater than or similar to 10(17) G. These results may have important implications for high-magnetic-field neutron stars and white dwarfs and, in general, in nuclear astrophysics when the system is embedded within a strong magnetic field.

A Probe for the Selective and Parts-per-Billion-Level Detection of Copper(II) and Mercury(II) using a Micellar Medium and Its Utility in Cell Imaging

A novel colorimetric probe 1 based on the picolyl moiety has been designed and synthesized. Probe 1 is composed of a pyrene and a bispicolyl amine (BPA) unit, in which the BPA moiety acts as a binding unit and the binding phenomenon is sensed from the changes in the signaling subunit. The probe detects Cu2+ specifically in water and both Cu2+ and Hg2+ efficiently in neutral Brij-58 micellar media. The probe shows a color change visible to the naked eye upon addition of metal ions. Notably, in a micellar medium, probe 1 can detect both the Cu2+ and Hg2+ ions even at parts-per-billion levels. Furthermore, the probe shows ratiometric detection of both the metal ions making the sensing quantitative. The two metal ions could be discriminated both visibly under a UV lamp and with the use of fluorescence spectroscopy. The probe could be also used in biological cell lines for the detection of both Hg2+ and Cu2+ ions.

Tuning photoinduced terahertz conductivity in monolayer graphene: Optical-pump terahertz-probe spectroscopy

Optical-pump terahertz-probe differential transmission measurements of as-prepared single layer graphene (AG) (unintentionally hole dopedwith Fermi energy E-F at similar to -180 meV), nitrogen doping compensated graphene (NDG) with E-F similar to -10 meV, and thermally annealed doped graphene (TAG) are examined quantitatively to understand the opposite signs of photoinduced dynamic terahertz conductivity Delta sigma. It is negative for AG and TAG but positive for NDG. We show that the recently proposed mechanism of multiple generations of secondary hot carriers due to Coulomb interaction of photoexcited carriers with the existing carriers together with the intraband scattering can explain the change of photoinduced conductivity sign and its magnitude. We give a quantitative estimate of Delta sigma in terms of controlling parameters-the Fermi energy E-F and momentum relaxation time tau. Furthermore, the cooling of photoexcited carriers is analyzed using a supercollision model which involves a defect mediated collision of the hot carriers with the acoustic phonons, thus giving an estimate of the deformation potential.

Design, Development and Calibration of HTS Wire Based LOX Level Sensor Probe

For space applications, the weight of the liquid level sensors are of major concern as they affect the payload fraction and hence the cost. An attempt is made to design and test a light weight High Temperature Superconductor (HTS) wire based liquid level sensor for Liquid Oxygen (LOX) tank used in the cryostage of the spacecraft. The total resistance value measured of the HTS wire is inversely proportional to the liquid level. A HTS wire (SF12100) of 12mm width and 2.76m length without copper stabilizer has been used in the level sensor. The developed HTS wire based LOX level sensor is calibrated against a discrete diode array type level sensor. Liquid Nitrogen (LN2) and LOX has been used as cryogenic fluid for the calibration purpose. The automatic data logging for the system has been done using LabVIEW11. The net weight of the developed sensor is less than 1 kg.